For returning players, here is a very coarse list of recent changes to the game that you should know about:

Previously, missions could only be started and completed when all players were present in the game. If a player left mid-mission, this would restart the mission for all of the remaining connected players. Additionally, players could not join mid-session.

Thankfully the developers are on point and have fixed this flaw. Players can now connect and disconnect at any time during a mission without interrupting the flow of the mission itself. This has also lent a hand in developing the reinforcement system:

By default, the game now allowed players to reinforce any remaining players left alive (though this can be turned off if desired). Once a player dies, a reinforcement timer of 30 seconds is started. Any players dying during the reinforcement timer will join the reinforcement queue with any other dead players (i.e; player two dies, and waits 10 seconds. His reinforcement timer reads 20 seconds. Player 3 dies at this time, they must wait 20 seconds before rejoining instead of 30).

Once the reinforcement timer expires, all currently dead players spawn in the airlock. The same system of loosing all suit upgrades exists on death, which is still a supreme disadvantage of dying. With this system, unlucky players can still participate in the rest of the mission without having to wait for a new one to start.

If all players die before the reinforcement timer can expire (i.e if everyone dies within 30 seconds of one another), the mission will still fail as normal and all players are returned to the lobby screen.

Ammunition is no longer color-based from each armory. Previously, each armory dispensed specific ammunition, and the different color of the ammunition determined its damage and rate of fire. This system has been done away with, and all armories now dispense the same ammunition. Ammunition damage and the rate your ammunition is restored by an armory is now based on the number of rescued civilian scientists (explained later).

A marine's ammunition always starts full now (500/500 rounds) instead of at 80% (400/500 rounds). In addition, the ammunition capacity suit upgrade was decreased to +100 maximum ammunition per upgrade from +250. At its maximum, you now have 900 rounds available.

Players can now bring two different weapons into a mission with them, lending to some excellent combos for different situations. These combos are predetermined and selected from a drop down list in the lobby screen. By default, you can swap weapons with your Tab key. All weapons still draw ammunition from the same pool. The weapon LED display now shows the rate you restore ammo from an armory, your current ammo pool, your maximum ammo, and the current grade of ammo (light, medium, heavy, etc).

During development there was a test mode called "Rescue", which existed alongside "Salvage". This has been done away with as separate game modes; elements of the Rescue game mode were combined with Salvage. Civilian scientists now exist as part of the map's generation. These scientists can be escorted back to the airlock to raise the team's science score, which in turn improves the characteristics of everyone's weapons and ammunition.

The scientists initially exist inside camouflaged panic rooms, which exist within a new area of map generation called Labs. Labs can be told apart by specifically textured doors, as well as a general lack of cores and usually breaches (random breaches can still exist within labs). Labs typically also have very few doors, leading to (typically) wide open areas. The panic rooms always have the same texture, thus can be told apart from surrounding walls. In addition, if an Xeno is close to a scientist, you can hear them panic and cower. Scientists show on your radar in the same color as your current HUD color (if moving, or with maximum radar range, they show up all the time). Xenos cannot breach panic rooms, thus scientists are safe so as long as they remain in the panic room.

Once you open a panic room's door, the scientist behind it is released into the map proper. The scientist will attempt to follow closely behind you, but they will back away from Xenos and gunfire. This can be problematic when trying to lead them through crowded or hostile areas, but that's part of the challenge. Once the scientist gets within view of the airlock, they will automatically run to it, open the door, and despawn. This awards your team one science point.

Each rescued scientist increases the amount of ammo you restock each tick from an armory by three (from the base of ten). This increases up to a maximum of 500 (essentially depleting the entire armory in one go) which is fairly ridiculous. For every four scientists (at the landmarks of 4, 8, and 12), your ammunition's power increases one grade. You start at orange (the weakest), then upgrade to Magenta, Blue, and finally Green (the strongest). Higher grades of ammunition do more damage than the previous grades. Science is awarded for the entire team, and science carries over between missions so as long as one player survives the mission. The host's science is used when hosting a game.

Map generation has been consolidated loosely into what was the "corridors" generation mode. No longer are there explicit options for Mazes, Minimazes, or Dungeons. This appears to have resulted in a more consistent randomized map instead of wildly varied and usually extremely difficult.

Map generation can be explicit or randomized, and a great many options can increase or decrease the difficulty of the game for the players. Experienced parties may typically play on 'Randomize All' for the 'true' experience of the game, whereas it is advised for newer players learning the ropes to tone down some aspects of the map to facilitate learning.

Seed is used by the map generation software to determine the mathematical computations that will generate the map. Using the same seed and the same settings will always result in the same map each time. In "Random" mode, a random hexadecimal number is chosen as a seed for you, but you can still choose specific settings. In "Explicit" mode, you define a specific seed to play on. In addition the game will allow you to preview the map that has been generated from the seed. In "Randomize All", all settings are completely randomized.

These settings coarsely affect map generation:

Infestation - How much alien gunk appears on walls, set to either "off", "less", or "more". The gunk is mostly cosmetic but can make it more difficult to see where door controls, consoles, and breakers are on the walls.
Doors - How many doors appear on the map. "More" will make them appear at almost any time the corridor turns or ends, and at the entrances to labs. "Less" will be the same as more, but every door only has a 50% chance of appearing. "None" does not allow doors to appear on the map.
Fences - How many electrical fences appear on the map. Fences by default will only appear in the middle of a corridor, never at the ends of it like doors. "More" makes them appear at almost every two open spaces in a corridor. "Less" gives them a 50% chance of spawning normally. "None" will not allow fences to appear on the map.
Invert Barriers - With this option turned on, fences will appear where doors spawn, and vice versa. This will make fences occupy corridor ends while doors occupy the middle of them. This can make it very easy to seal areas off with fences.
Room Setting - This tells the generator how to deal with open spaces left by generation. "Empty" leaves the spaces as they are. "Pillars" puts some walls in the middle of open spaces to cut up sight lines within the room. "Filled" tries to completely fill the rooms with alternate walls, at most leaving a one by two corridor.

These rules affect the spawning of aliens and sentries, as well as rules for determining power outages:
Sentries - Toggles the presence of sentries on the map. Sentries typically occur at any bend or intersection of a corridor that is not already occupied by something else.
Power Start - Whether or not the power is activated on mission start.
Random Breaches - Hardmode on or off. Normally, breaches will only occur at the dead ends of corridors allowing you a good idea of where they'll show up and ways to seal them off or suppress them. With random breaches, as the game progresses, breaches can appear on any tile in the map (unless that tile's occupied by a sentry). This can make navigating even basic areas hazardous.
Astro-creeps - Turn these pains on or off. They're little alien blob things that you see running on walls that are hard to hit but don't kill you instantly. If one jumps on you and isn't shot immediately, they'll damage a random system. They blind you while attached and are prime shenanigans for causing friendly fire incidents. They can also distract your attention from the bigger, nastier xenos that they usually accompany.
Difficulty - The speed of breaches and enemy spawns, ranging from easier to insane. Higher difficulty makes breaches appear faster and enemies spawn from them faster. Two special settings, "random each" and "random all" exist for the RNG inclined. Random All will choose the frequency of breaches, then divide that by three, arriving at a number between 3-20. "Random All" chooses random numbers for both breaches and spawns.
Power Failures - How often the power fails and you must blunder around in the dark looking for a breaker. There's three primary settings, "Off", where failures never occur, and then time and interaction based.
Time based failures have a 50% chance of occurring at a predetermined time between two settings, from 30-60, 60-120, and 120-240 seconds. The game will pick a number between the setting. After that many seconds, the game will flip a coin to see if the power goes out. After that it chooses another number and the cycle repeats.
Interaction based failures have a chance of occurring whenever you interact with a door, console, fence, or really any other device. They can be chosen in a 1/8, 1/16, or 1/32 chance of occurring on interaction.

Party settings have been introduced to be separate from the other groups of settings, mostly so they aren't randomized during "Randomize All".

Friendly Fire - Can be on or off. This only affects taking damage from other marines. With friendly fire off, the disorienting effects of getting damaged still persist, such as your screen flashing and disorientation. The only difference is that you take no systems damage.
Reinforcements - On or off. If reinforcements are enabled, dead players all respawn in the airlock (albeit without any upgrades) after a 30 second timer from the death of the first player. The first player to die must wait 30 seconds before rejoining, while any players who die after the first player must wait whatever time remains. If all players die before reinforcements spawn, then the mission fails as normal. Without reinforcements, any player that dies will stay dead until the mission ends.
Private Party - Having your party hosted as private allows only steam friends to join your game. Otherwise, any player in the public lobby can join.

Various consoles are sprinkled around the map for you to use and help you kill alien scum.

The ever important. Your primary objective is to download every one of these on the map, then get to the reactor and blow it without getting blown up yourself. Downloading a core takes ten seconds, unless you have a download speed upgrade, which reduces this time by two seconds for every upgrade. After downloading a core, every player on your team recieves a random upgrade to their systems. If you already have the upgrade that the game randomly selects for you, then you get no upgrade. Sucks to suck.

The number of cores on the map can be anywhere from four to 60. Your suit automatically shows you the distance to the closest core (but not the direction) unless there are no cores left (in which case it shows you the distance to the coolant) or the power is out (then it shows you distance to the nearest breaker). Alternatively, if the station happens to be in the middle of a reactor meltdown, this text will show you the distance to the airlock.

These hold 500 rounds of ammunition each. By default, they restore 10 ammo per tick while being interacted with. This interaction is interrupted when moving away or firing your weapon. All marines start will their maximum load of ammunition at the start of a mission. Armories are unique in that they do not benefit from download speed upgrades, but rather benefit from accumulated science.

Each rescued scientist increases the amount of ammunition you receive each tick by three, up to a maximum of 500 (essentially draining the entire armory at once, which is ludicrous). For every four scientists (up to 12 total) rescued, your ammunition's damage is increased.

These stations each have four uses available to them and can repair systems damage sustained to your suit. For every system damaged, you'll need one individual repair. As of a recent update, repair stations will now repair as many systems as they can when you finish interacting with them, using as many charges from them as systems that were repaired. Thankfully, these repair stations benefit from the download speed upgrade, allowing you quick repairs if you have it at a high level. You have six systems capable of taking damage:

Text - Loosing this disables all text on your HUD. You'll still be able to see your HUD's icons, but anything that uses text will not be displayed. This includes distance hints to breakers, datacores, coolants, the airlock, and warnings for enemy proximity displayed above the map, as well as the general log and chat.
Icons - Disables all icons on your HUD, including crosshair and aim assist, if activated. Your map is a separate entity and is not disabled.
Map - The Map is removed from the HUD. This can put you in trouble if you need to rely on it to find your way around or find your way to a repair station. The map also shows where your teammates are, so if one of them rounds a corner and you don't know they're there, you might blast them by accident.
Flashlight - God won't save you if the power goes out when you loose this. Not a big deal with the power on, but when it's off you'll be stumbling around in the darkness flailing your arms around for a breaker and firing at random into the darkness hoping you don't get eaten. Unless you have infravision, in which case you'll probably find a breaker before you loose battery power.
Infravision - Turns your infravision into a fuzzy mess and makes it unusable. Not a big deal if you still have a flashlight or the power is on.
Ammo Display - Disables your weapon's ammunition display and (sometimes thankfully) the low ammunition alert tone. If you still have your HUD then this isn't a big deal since you can still see how much ammo you have left total.

There's always four of these and they're always inside the reactor core. First, you have to download all Datacores on the map to access the reactor shields. Then, after raising the reactor shields, you interact with the coolants just like a datacore. Coolant consoles benefit from the download speed upgrade. After disabling all four coolants, you have 90 seconds until reactor detonation.

Better find your way back to the airlock quick, and better figure out which person has the airlock pathfinder upgrade before you follow some random in the wrong direction.

Your handheld weapon is what you use to defend yourself from xeno scum. All weapons share universal ammo and have a display to indicate how much ammo remains with you. Weapons do not require reloading.

All projectiles are capable of ricocheting at oblique angles (50% chance), which can be helpful in narrow corridors to help redirect poorly aimed shots. They can also unexpectedly bounce around and hit you and your teammates. Projectiles will always ricochet when hitting an active laser fence, which can be dangerous and lethal to your friends and yourself. Mind your fire if you shoot down a hallway with a laser fence at the other end. This is especially hilarious if using a shotgun.

Your weapon's display shows the rate you replenish ammo from an armory, your current grade of ammo (light, medium, heavy, and heavy(er), increasing in damage), ammunition remaining, and your maximum ammo capacity. All new players start with a full load of ammunition. Ammunition can be replenished from armory cores, which are scattered around the map. Each armory contains 500 rounds of ammunition.

If you take damage, it's possible for your weapon display system to be disabled. This in itself is not a big deal as long as your Text System is not destroyed as well, as you'll still be able to keep track of your ammo with your HUD. The reverse is also true if your HUD's text system is destroyed but your weapon display is intact.

In the lobby screen, you can choose from any combination of two of the five different weapons: Rifle, Shotgun, Razor, Hammer 2x, and the Hammer 4x. Weapons by default can be switched between in-mission with Tab. All weapons draw from a shared ammo pool.

The Rifle is the default choice and is well rounded for most situations. It has dependable accuracy and fire rate, and only moderate recoil, allowing it to be shot down hallways with relative ease and is still able to mop up aliens in close quarters. It is hard to go wrong with the rifle, however it is not as good as a specialized weapon in some applications. With upgraded ammunition, this weapon simply deals much more damage up front.

The Shotgun packs a punch at close range and consumes eight ammunition per shot. This makes visiting Armories more frequent, but the weapon can obliterate two or more xenos at close range with a single shell. Due to its high damage it can be very useful and reliable around corners and at close range to blast an xeno apart just before it gets to you. Due to the spread of its pellets, it is forgiving of poor accuracy, and can even make hitting small Astro Creeps at a distance an easy task. The weapon suffers at range due to the inherent spread of the pellets, however the rounds can ricochet off of walls back down a corridor and still deal good damage. It also suffers with a low firing rate -- two well placed xenos or a missed shot can still make quick work of you. The shotgun probably benefits the best from upgraded ammunition: if so much as two pellets graze an alien, it gets turned into paste, no matter the distance. This can make killing enemies a long ways away in a narrow corridor even easier. At close range, the pellets can pound dense groups of aliens.

The Razor is a sub-machine gun and has a higher rate of fire than the Rifle, but is clumsy with recoil. This allows it to have more damage output than the Rifle, but makes it more difficult to aim and use at medium and long range. This makes it more useful in closer quarters where higher damage can clean up enemies faster. This weapon becomes even better at close range with upgraded ammo. The only downside to this weapon: the clumsy recoil and rate of fire gives it a propensity to chew through ammo.

The Hammer 2x and Hammer 4x work like marksman's rifles. They fire two and four shots respectively in a tight group (consuming two and four ammo), allowing better precision and damage than the rifle per shot, however the weapons suffer from much lower rate of fire. Recoil with them is high, but manageable due to the low fire rate or with timed shots. The 4x deals more damage and has a slower fire rate than the 2x, and may be preferable over longer ranges. The 2x can be more useful in tighter corners, but still maintain some long-range utility. This behavior makes it much easier to splat xenos at a distance, but these weapons suffer in close quarters. It is usually best to switch to an off, non-hammer weapon for closer jobs (unless you took both Hammers, in which case you are an absolute madman). With upgraded ammunition, the Hammer 4x quickly splats anything with a solid hit. The Hammer 2x may still need an extra shot or so, but it is still just as capable at maximum damage.

Support structures like Doors, Fences, and Sentries are all spawned on map generation. They also can all be disabled with specific map settings, so they are not always guaranteed to appear on the map to help you. Several map upgrades exist to help show the location and status of barriers and sentries.

Doors can provide temporary protection by delaying xeno advance and sealing off areas temporarily. Every door has a LCD above it showing what its number is and whether it is open (+) or closed (-). The door's numeric can be used to keep track of it even if not in view of it, as you'll get a text notification when a door is cycled or destroyed (shows up in the log as "DOOR [door #] COMPROMISED"). This can let you know when a door used to hold back Xenos temporarily has been broken. When a door is damaged by an xeno, a very noticeable sound cue plays, and the door's display will also briefly flicker with the remaining integrity of the door. There's also a display on the side of every button panel for doors indicating the remaining integrity. Doors that are damaged will also warp and bend.
When facing the door from any side, the control panel for it is always to your right. If you're running through a door and need to close it behind you, to your left will be the control panel on the other side of the door that you can smack while sprinting through it.

On the map, (if you have the proper upgrades) doors will be displayed with their open or closed status, or a shattered icon if they have been compromised. When power is disabled, doors can be "pushed" open by walking into them, allowing you to pass through them. Closed doors can also be pushed open by xenos without being destroyed while there is no power. Doors that are half opened by pushing will close when power is restored.

Sometimes, it is best to leave a door blocking a breach or similar area open until it is needed. Every time a door takes damage, that damage is permanent. The door is buying you a set amount of time whenever it takes a blow from an alien. This can be especially important around a crowded reactor (along with sentries). It is not always best to seal an area or activate a turret before it is needed, as occasionally you will have time-sensitive work that needs doing and too many xenos around to do it.

Electrical fences will damage anything that attempts to pass through them when activated, and can instantly kill xenos, effectively sealing the area behind it. If you're lucky, a fence may spawn directly in front of a breach, allowing you to nullify that breach as long as power remains on. They are far more effective than doors as they cannot be passed by xenos as long as there is power. Fences are also a great tool to shred large buildups of aliens. Any fences that were enabled before power outage will turn back on when the power is restored, so avoid standing in them lest someone else stumble into a breaker while you're doing so.

Fences also have a unique property of always reflecting any projectiles that strike them while it is activated. This can be very dangerous (fun) for you, your friends, and the xenos. Get creative with bouncing bullets. Avoid shotgunning yourself at close range.

Ceiling mounted turrets spawn on the map that can be activated to help automatically kill aliens that are within their range. They are activated by interacting with their attached console, and take 10 seconds (without upgrades) to turn on. Getting a download speed upgrade will contribute to turret activation speed.

Turrets can identify friend or foe and thankfully avoid shooting at you if there's a you between it and an enemy. They'll emit a loud beeping tone if you're in their line of fire, warning you to either get out of the way or shoot what it's trying to shoot at. Key word in this situation however is "avoid". Walking into a turret's line of fire while it's shooting will likely result in systems damage or death. A turret's projectiles are also perfectly capable of bouncing off of walls and fences, striking bystanders, so be mindful of where you're standing. In addition, turrets now come with a laser sight to help better identify what they're shooting at.

They also have a limited ammo capacity (400 rounds) before their supplies are exhausted and they deactivate. There's no way to resupply them, so use the time they buy you wisely. A single turret can easily cover a breach for some time while you go and do important spaceman things. It may be better to leave a turret deactivated for the time being if you believe the time it buys you is better spent later in the mission.

Xenos taking damage from firearms are also subtly pushed by the projectile: this is made more obvious if you're behind an enemy a turret is trying to shoot at. Turrets can end up either shooting you by accident or pushing an alien into you if you don't mind your distance. Try not to be in the background of a turret's engagement wherever possible.

Upgrades are awarded to all players when a datacore is downloaded. All players will individually recieve a random upgrade. If you already have the upgrade (or are at maximum level for that upgrade) when awarded it, you're bum out of luck and get no upgrade from that core.

When activated, the "ASSIST" text below your crosshair is activated. All enemies within a short range (about five to ten meters or so) will have a hexagon with an exclamation point displayed on your HUD, allowing you to target them through darkness, smoke, gibs, or other vision obscuring effects. Despite its short range, it does work through doors and walls, allowing you a good idea of how many xenos are on the other side of them.

This upgrade is immensely useful as it allows you to still target enemies through smoke and haze, and gives you a better idea when to start and stop firing, even if your vision is obscured, and especially during outages. Its only downside, it can only tell you what you're already looking at. It doesn't cover your behind.

Starts at 10 seconds. Decreases the time it takes to interact with Sentries, Data Cores, Repair Stations, and Coolant Consoles by two seconds for each upgrade, to a minimum of two seconds. Immensely helpful as you can download cores or activate sentries and move on very quickly.

Hope that you get blessed by the Techpriests, this is possibly the most useful upgrade. This allows you to deactivate coolants, turn on sentries, download cores, and repair yourself many times faster than you are normally able, which usually makes the difference when trying to download difficult to reach cores or move through time sensitive areas.

Starts at 2.5 charge per second. Increases the amount of battery power you receive per second while interacting with a console by 2.5, to a maximum of 12.5. Your battery power is used to power Infravision and your flashlight, both of which will become increasingly less effective as your power is consumed. Infravision will begin loosing resolution, and your flashlight will begin to cover less area, eventually dimming to a shade of red and only a narrow cone. Interacting with any console (Coolant, Data Core, Armory, Repair Station, Sentry) will charge your suit during the duration of interaction.

This upgrade falls squarely in the middle of "somewhat useful" and "could probably live without". The only time this comes in handy is when your visits to consoles are infrequent (which only happens if you're holding down an area or scouring labs for scientists). Even then, this just makes it so you can juice up from less consoles. If you're regularly bouncing from console to console, your battery capacity will stay at maximum anyways. Even during outages, a modestly skilled player can still survive long enough to fight to a breaker without much battery power, unless in an inopportune area. Interestingly enough, this upgrade becomes less effective as you get Download Speed upgrades, as having a download speed upgrade will make you spend less time interacting with consoles (except armories, but the same could be argued with increasing your science).

Starts at 60 seconds. Increases the amount of battery power you can store by 30 seconds, up to a maximum of 180 seconds. When receiving this upgrade, you get a free 30 seconds of battery power automatically. I haven't been able to test it, but apparently any time you receive an upgrade, you also get at least 30 seconds of battery time.

This upgrade is more useful then Battery Recharge Rate, as it allows you to stay topped off and away from consoles much more comfortably, and for longer duration. Still, a lot of other upgrades (i.e download speed) can be much better.

Initially, your map starts with nothing but the relative location of you and your teammates. Map upgrades always progress from bottom-to-top: Floors, Barriers, Data Cores, Breaches, Sentries, and finally overview. For each level:

• Floors: Areas you have personally been to will be revealed on your map, helping you keep track of where you have already been. It should be noted, the game tracks where you have been even if you don't yet have the Floors upgrade. Once you get the upgrade, all explored territory will automatically be revealed for the current map.
  
• Barriers: The locations and status of Doors and Fences in explored territory are shown on the map. Doors show their status as either open, closed, or breached, while fences are shown on or off.
  
• Data Cores: Any data cores (Data Cores, Armories, Repair Stations, and Coolants) in explored territory are revealed on the map with an appropriately-colored square.
  
• Breaches: A pulsing purple square is shown over the location of any Xeno breach in explored territory.
  
• Sentries: A green square is placed on any explored and inactive sentry on the map. This turns to a green diamond for activated sentries, and the diamond pulses when the sentry fires.
  
• Overview: All map territory is automatically explored without having to visit it first.

Your map is your lifeline, and helps direct you where to go. It can be very helpful to locate cores and points of interest that are close to you, but obscured by walls. Combined with the Pathfinder upgrades, it can make finding your way around any map relatively easy, minus the fact Xenos may try to kill you while traveling.

Pathfinder upgrades show indicators on the map of the correct intersection to move to in order to make it to the nearest object of that type. Pathfinder upgrades are randomly awarded, and do not progress through a strict system like the Map Data upgrades. Pathfinders are available for:

• Active Coolants - dark blue square outline
  
• Active Data Cores - light blue square outline
  
• Inactive Sentries - green square outline
  
• The Airlock - white cross
  
• Stocked Armories - yellow square outline
  
• Stocked Repair Stations - red square outline

In addition, the outlines on the map do not completely overlap one another, so you should be able to read all available pathfinder upgrades, even if they are all on the same tile. It should also be noted that the pathfinders will only lead you to consoles that can be interacted with -- it won't lead you to already downloaded data cores or depleted armories.

The Airlock pathfinder is extremely useful in the 90 seconds you have to escape the ship during detonation as it can lead you directly back to the ship. If you have this upgrade make sure you're the one leading the group back. The other pathfinders are great to have whenever the need may arise for what they represent.

Infravision starts unusable, at 0%. Each upgrade increases effectiveness by 25%, up to 100%. At its basic level, your infravision is grainy and has low picture quality. The sharpness of the picture improves as it is upgraded, though it is still coarsely usable at 25% in chaos and confusion.

While useful in a pinch (i.e being without your flashlight), infravision is frequently forgotten about since it makes everything really, really bright. It's usually easier just to use normal vision, though everyone has their preferences. In addition, if you scour the options, there are three different 'versions' of infravision you can use, appropriate to your taste: Greyscale (black and white thermal style), night vision (phosphorescent green), and predator (a color scale thermal vision from blue [cold] to red [hot]). Infravision also no longer consumes three times as much power while active like it used to, it consumes the same amount of power whether active or inactive.

Starts at 500 rounds. Increases by 100 rounds for each upgrade, up to 900 rounds total. A marine always starts a mission with his ammunition at its maximum capacity.

As basic an upgrade as it is useful. This simply lets you splat more Xenos in one go without needing to find an armory. With only 500 rounds capacity, holding down busy breaches can require frequent excursions for resupply. With 900 rounds, those excursions are approximately 1.8 times less frequent.

The motion tracker has four tiers of upgrade:

• None: The motion tracker pulses your map when it detects an enemy, frequency based on proximity of the enemy. A text hint above your map will warn you of motion, and its distance from you, within ten meters of your position. This upgrade does not reveal the direction of the enemy, only their proximity. Discovered civilians within 10 meters are also shown on the map. Their color is the same as your current HUD's color.
  
• Short: All features of the basic tier. In addition, the tracker now shows the enemy's exact location on the map within 10 meters, each enemy represented by a white dot. Since at the time of writing, the enemy is always moving, the enemy is always shown on your map.
  
• Long: All features of the short-range tracker. In addition, the tracker can now track motion of the enemy and civilians across the entire map. Entities outside the ten meter range of the map are shown on the edge of it.
  
• Civilian Tracker: All features of the long-range tracker. In addition, any civilian (discovered or still hiding in a panic room immobile) are revealed on the map.

The motion tracker is possibly more useful than download speed, even at its first upgrade. With the short-range tracker, you can simply watch the map to keep your back covered, instead of needing to watch two directions at once. This can also give clues as to the location of breaches, as well as how dense the enemy is in a particular location.

The name of the game is perma-death. If you complete a mission, you keep all upgrades and ammunition and carry it over to the next mission. If you die, you loose everything and start with a fresh recruit with no upgrades. By default respawning is now enabled. Provided all party members don't die within 30 seconds, all dead players will respawn in the airlock without any upgrades. Still, be mindful of how you play and what you point your crosshair at.

The maps are intentionally claustrophobic, requiring you to have careful positioning between your team and be mindful of your aim. Don't run in front of someone's field of fire, and don't shoot so close to your buddies. Running in a group of four is fairly useless as hallways are at best, one and a half men wide. Groups of two are much better, and sometimes splitting up and searching for clues (as a gang) is the best, as it allows you to cover the most ground (and hence, usually get the most datacores).

Sentries, Fences, and Doors can typically watch your back for you. In lieu of these you may want to travel in a team, just be careful not to step on one another's toes. Clearing the way through a breach can be made easier with twice the firepower, but just be careful of your teammate trying to get shots in or move past you. In other cases, sometimes you might want another teammate to breach a room together. One person can handle one direction, so all you have to do is clear enough aliens out so the both of you can get a foot in the room and cover a separate direction. Once this is accomplished, both of you can move out of the hallway, and further into the adjacent rooms, cleaning up from there. Just be careful not to abandon your pal's backside.

Using 1, 2, 3, and 4 on your keyboard can be used to see your team's points of view in different amounts of intrusiveness. 1 turns all views off. 2 will place the three views on the right of your screen, small but enough to see in general what they're looking at. 3 will shrink your screen slightly and place your team's views on the bottom of the screen in a row. 4 will create classic split-screen gameplay and allow a mostly equal view of everyone's screen, giving you a good view of what upgrades each player has and even being able to read their version of the map (in the case that they have an upgrade you want to use).

Let teammates with better upgrades in what you're trying to do take care of it. Someone who has been blessed by the Techpriests with high download speed should be giving the Data Cores the succ (imagine steam censoring the word $ucc) very high amounts of suction and activating sentries.

Adrenaline mounts in your marine the closer they are to danger. Being nearby aliens begins to pulse your screen (if enabled). The closer your marine is to danger, the more adrenaline that mounts, which in turn increases your movement speed. Adrenaline can usually be used to outrun or gain some more space from xenos, and can be useful to jet into an area you need to be in (like behind a fence). Backpedaling reduces your movement speed, so avoid doing so if you need to scoot faster than you need to shoot.

Adrenaline also manifests during the final 90 second airlock sprint. The closer the timer is to reaching 0, the faster your character moves with purpose. Again, this is useful for being somewhere you need to be (in this case, the airlock).

Adrenaline and danger is coarsely represented by the intensity of the music. Music slowly ramps up from an idle/waiting bar on repeat to a more sinister or heavy melody. At the highest amounts of danger, stingers and suspense cords begin playing, indicating imminent death. The intensity of the music can be used to determine how close enemies are to you.

These guys are scattered throughout the map in new rooms, dubbed "labs". Labs have distinctive walls and doors, as well as an apparent lack of consoles throughout them. Civilians hide in panic rooms embedded into the walls of the labs. These walls are always the same, so they are easy to identify once you figure out what they look like. Once you open the panic room, it cannot be closed and the civilian is officially 'in play'. Open a panic room simply by walking into the 'door' of it, however be aware they cannot be opened while the power is off. Civilians can and will die by xenos or friendly fire, so mind your movement and shot placement in their proximity. You receive a -500 XP penalty if you kill a civilian by your own hand.

Once released from a panic room, Civilians will appreciably try to stay directly behind you, and will try to closely match your movements. Civilians are, however, easily frightened by gunfire and the presence of nearby xenos, in which case they'll move away from the source of gunfire (usually you) or the nearby xenos and cower. Once the source of their fear is gone, they'll resume trying to follow the player nearest to them. This can sometimes result in them following a different player, which can both be annoying and useful.

Retreating civilians (from gunfire or xenos) will automatically try to deactivate doors and fences blocking their path. This can be a good thing (if retreating from xenos with a scientist behind you, he can automatically open a path of retreat if played correctly), and usually a bad thing (leaving important defenses deactivated).

The goal is to get the civilian back to the airlock in one piece. Doing so increases your team's science by one for each rescued scientist. Each science point increases the rate armories replenish your ammo at by three (from the base of ten), and every four science points (up to 12) increases the damage of your weapons.

Naturally, sometimes it is not worth it or suicidal to try and get civilians out of the facility. Think of your own survival first when considering trying to get to civilians. Civilians are easily dissuaded from getting through areas safely by nearby breaches, or if you have to shoot to keep aliens back. If you have to shuffle them past an active breach, you'll have to be very quick about it. Most of the time, if an alien spawns before they get a good distance past it, the scientist will retreat away from you back whence he came, and the alien will usually go straight for him. Its not very feasible to try and get a scientist past anything more than one, possibly two breaches where they have to pass it in close proximity. It's usually not worth the risk to yourself.

Ranks and final score is measured by experience points, and they are your badge of honor. The Obituaries list on the main menu starts with your highest scoring marines and scrolls down, remembering every marine you ever embarked with. Brag to your friends of your high rank in a very not mainstream game that they most certainly have never heard of until now.

Your marine's score is cumulative so as long as they survive the mission. If at any time they die, your score, rank, and upgrades die with that marine. If they do survive, though, all of that is carried over to the next mission. Rank does nothing functionally, however your rank is branded on the back of your marine in-game so people know how much of a badass you are while staring at your backside. Ranks are only awarded upon mission completion. If you gather enough experience in-mission to get to the next rank, it won't show up until next mission.

Rank starts at Private, needing 10,000 experience to unlock. Each successive rank requires twice as much experience as the last to unlock (I.E: Private First Class is 20,000 exp total).
All the ranks I know of:
No Rank - 0
Private - 10,000
Private First Class (PFC) - 20,000
Corporal - 40,000
Lance Corporal - 80,000
Sergeant - 160,000
Gunnery Sergeant - 320,000

Actions that generate experience:

• Ammunition Expended: 1 XP - Per round of ammunition expended. For weapons like the Shotgun and Hammer 2x/4x that fire more than one round per shot, you are awarded XP for every unit of ammunition used to fire.
  
• Ammunition Restocked: 2 XP - Per round restocked.
  
• Time Alive In-Mission: 5 XP - Per second.
  
• Astro-Creep Kill: 10 XP
  
• Space Beast Kill: 20 XP
  
• System Repair: 175 XP - Per each system repaired (text, flashlight, etc).
  
• System Damage: 400 XP - Per each system damaged.
  
• Sentry Activation: 100 XP
  
• Datacore Download: 250 XP
  
• Coolant Shutdown: 500 XP
  
• Mission Completion: 10000 XP
  
• Civilian Kill: -500 XP
  
• Teamkill: -1000 XP

At the time of writing, there appears to be a bug where the only experience stats that are rolled over into your tour of duty are mission completions and time spent in mission. All other actions appear to be added together and summed to your experience at the conclusion of that mission, but are forgotten at the conclusion of the next.