You begin every mission by spawning in the Airlock. Your main objective is to download data on all the blue terminals, called Datacores. Once you're done, you must go to the Reactor Room, lower the Reactor Shield, and disable its Coolants to initiate a Reactor Meltdown.
Once the Meltdown is initiated, you have 90 seconds to reach the Airlock you spawned in before the ship explodes with you in it.
As you progress, more and more aliens will spawn on the map, and your resources will become scarce. The game may start off calmly, but time is of the essence!

Many settings can be played with to find the experience you prefer. There are some broad modes at the left of the screen:

• Random Seed: random map, but you can play with how many map elements are generated (datacores, sentries, etc).
  
• Explicit Seed: specific map. Replaying twice will give the same map.
  
• Randomize All: the map AND settings are randomized.
  
• Mission of the Day / Campaign of the Week: limited-time missions to progress through. CotW is an infinite sequence of preset missions that get progressively harder, and has a global leaderboard. You can see the leaderboard of previous Campaigns in the main menu.
  
• Kit Mode: Same as Randomize All, but you start with some completed upgrades, and downloading datacores does not give you new upgrades.
  
• User Mission: Explore some community-made maps.

If the gamemode you selected allows you to edit certain map/rule settings, you will see the following list.
Map generation

• Infestation: adds a sort of grime on the textures of the ship, partially covering switches and making it slightly harder to make out the geometry of the map. Xenomorphs may Lurk in Infestation (see below).
  
• Doors: generates doors that the user can open and close to block line of sight with aliens.
  
• Fences: generates fences that will kill aliens and damage users on contact.
  
• Barriers: "Normal" will generate doors at the edge of corridors, and fences between those doors. "Inverted" does the opposite.
  
• Rooms: "Filled" will fill the inside of a room to turn it into 4 corridors. "Empty" will leave the room completely open. "Pillars" adds 1x1 pillars inside that room, as a sort of in-between option.
  
• Sentries/Datacores/Armories/Repairs: control how often these elements will generate on the map.

Game rules

• Initial Power: If set to "off", the power will need to be turned on (by finding and interacting with a Breaker) before you can interact with anything else in the game.
  
• Reactor Safety Protocol: If set to "on", when the Reactor Meltdown is initiated, all doors and fences will open on the map.
  
• Breaches: "Normal" will only spawn breaches in dead ends. "Random" breaches will spawn them anywhere it can. Note that the number of breaches will be the same (as many as there are dead ends on the map).
  
• Astro-Creeps: Those little rascals climb up on your face and slowly damage you until you shoot them down. They die to a single bullet and spawn in waves with Xenomorphs.
  
• Beasts Lurk: Rather than roaming the map, Xenomorphs may choose to Lurk in a part of the map with Infestation. When they do, they will stop triggering motion trackers (from your upgrades and from the Security Table). They will start moving if you get close enough or shoot them. They are still easy to discern by using Infravision.
  
• Difficulty: Determines how often the game tries to open a breach or spawn more aliens. If "Random each" is selected, the game will regularly change the difficulty, meaning you'll have moments of calm followed by a ton of aliens spawning.
  
• Power Failures: Causes failures during which you need to find a Breaker to turn the power back on. These failures can be selected to trigger when interacting with any map element, or after a certain duration has elapsed.
  
• Friendly fire: allow damage between players. This does not prevent taking damage from sentries.
  
• Reinforcements: give players extra lives. Players have a respawn time, and if all players die at once, the game is over. As such, this option and the option above are only for Multiplayer.

Below is a list of all elements that can be generated on the map, as well as a short explanation of their purpose.

• Airlock: This is the entrance and exit of the map. Marines will begin their mission here, will respawn here in the case of Reinforcements, and must reach this door again before the end of a Meltdown.
  
• Door: This door can block line of sight between players and aliens, preventing them from following a player. Note that if a Xenomorph sees you before closing a door, they will ram into it and eventually break it open.
  
• Fence: Fences do not block line of sight, but will kill any alien that tries to cross it. Players take one point of damage (lose one Upgrade or one System Component) if they cross the laser fence while it is on.
  
• Datacore: These are the game's primary objective. Downloading their content may net you an Upgrade (or even a Devlog entry!). Once all datacores were downloaded, you will be able to turn off the reactor's Coolants.
  
  
• Sentry: Once turned on, sentries will fire at any moving aliens up to a certain distance. They have limited ammo, aim automatically at any angle, and will make a beeping noise when a marine is in the way rather than shoot through them. It's still possible, however, to run into a sentry's bullets and receive damage.
  
• Repair: These stations will repair any missing System Components you may have, and can only repair up to 4 points of damage each. If you have several components to repair, the station will repair as many of them as possible at once.
  
• Armory: These stations hold a limited amount of ammunition and let you refill at anytime. Unlike other terminals, shooting will stop the interaction, and the refill rate is not determined by the Download Speed, but by Science Points (see "Scientists" below).
  
• Reactor: This unique element in the game is the last objective you need to complete before leaving. Once all Datacores have been downloaded, you must lower its shield to gain access to the Coolants. Turning them off will initiate the Reactor Meltdown.
  
• Breaker: These are essential to fixing the station's power during an outage. When the power is out, your HUD will stop monitoring the distance from the closest Datacore, and will instead monitor the distance from the closest Breaker.
  
• Breach: These sparking holes in the ceiling are the Beasts' spawn points. Occasionally, waves of Xenomorphs (and possibly Astro-Creeps) will crawl from that hole and start roaming the station.
  
• Security: This unique map element, if found, will display the entire map of the game, along with flashing white dots (Xenomorphs) and flashing green dots (Scientists).

As you download more datacores (or by default if you're playing Kit Mode), you will obtain Upgrades to your character, which are visible on your HUD. Taking damage may remove random upgrades, while being killed will remove all of them, giving you a completely new character.
Whenever you download a datacore, the game has a random chance to select a random type of upgrade. If this type is already fully upgraded, you do not receive any upgrades. As such, the more you progress, the less likely you are to receive upgrades.
There are 9 types of upgrades, for a total of 37 upgrades:

• 1 - Map (None / Floors / Barriers / Cores / Breaches / Sentries / Overview): Reveals certain map elements on your radar as you approach them. "Overview" shows the same map elements as before, but does not require you to approach them first.
  
• 2 - Download Speed (10 / 8 / 6 / 4 / 2): How fast you interact with Datacores, Sentries, Repair stations and Coolants. Armories have their own stat (see Scientists) and are not affected.
  
• 3 - Battery Charge Rate (2.5 / 5 / 7.5 / 10 / 12.5): How fast your battery recharges when interacting with a terminal or a breaker. Battery gives you a brighter flashlight and Infravision.
  
• 4 - Battery Capacity (60 / 90 / 120 / 150 / 180): How long your battery lasts without recharging it.
  
• 5 - Infravision (0% / 25% / 50% / 75% / 100%): How intense the contrast of your Infravision is (default R to toggle). Infravision drains your battery life 3 times faster.
  
• 6 - Ammo Capacity (500 / 600 / 700 / 800 / 900): How much ammo your guns can carry at once. Ammo is shared between your two weapons (default TAB to switch weapon).
  
• 7 - Motion Tracker (None / Directional / Short / Long / Scientists): The "Directional" tracker lights up sections of your radar to indicate movement in that direction. "Short" and "Long" will add flashing dots where xenomorphs are found, while "Scientists" lets you see scientists hiding in safe rooms.
  
• 8 - Pathfinders (Airlock / Repair / Sentry / Reactor / Armory / Datacore): These upgrades can be obtained in any order and will add a marker on your map for shortest path to each of those elements.
  
• 9 - Aim Assist: This upgrade has only one level, and will display icons on top of every nearby alien, making it much easier to see them in the dark or while firing.

If you are hurt by something other than a Xenomorph or the Reactor Meltdown (Sentry, Laser Fence, Astro-Creep or Friendly Fire), the game has a 50% chance of either removing one of your Upgrades, or damaging one of your System Components. If you have no system components remaining, a beeping noise will play, and any source of damage may now be lethal.
The system components are listed in the lower-right corner of your HUD, and losing them has the following impact:

• Infra: disables Infravision entirely.
  
• Weapon: the ammo counter on your weapon is no longer visible.
  
• Icons: HUD upgrade icons are no longer visible. May also disable icons from Aim Assist (need confirmation)
  
• Tracker: disables your radar entirely.
  
• Lamp: disables your flashlight.
  
• Text: Removes all text from your HUD.

Note that in Kit Mode, losing an Upgrade will remove all its levels at once (for instance, Download Speed will go from 2s to 10s instantly), while you will lose levels one by one in other gamemodes.

There are two types of enemies in the game: Xenomorphs and Astro-Creeps. Both enemies will roam the map in random directions until a player or scientist is in line of sight, at which point they will start tracking them.
A Xenomorph in its... natural habitat?

If a Xenomorph reaches a player, a death animation will play where the xenomorph stands on top of and mauls them. Killing the Xenomorph in that animation will not save the player. Astro-Creeps, on the other hand, latch onto the player's face, and progressively deal damage to them, until the player shoots one bullet in any direction to kill them. These are relatively harmless alone, but can greatly confuse the player and make them more vulnerable to Xenomorphs.
An Astro-creep on its natural habitat... your face!

A player may block line of sight with aliens by closing a door, however Xenomorphs touching a door will damage it overtime, and a door that was burst open by Xenomorphs cannot be closed again. Note that Xenomorphs will also damage doors they encounter while roaming the map, meaning a breach behind closed doors is never fully safe.
When a Xenomorph is in an area of the map covered in Infestation, it may choose to Lurk. Lurking Xenomorphs are completely idle and will not trigger your motion tracker (neither the sound nor the white dots on your HUD or on the Security table). They will stop lurking once they are approached or shot.
Aliens of both type will completely ignore map hazards. Whether they're being shot by Sentries, or a Laser Fence is in their way, they are either roaming, following a player/scientist or lurking.

Scientists are human NPCs that may occasionally spawn on the map, hiding within Panic Rooms on the map. These are generated in the map's laboratories if there are any. Scientists are unarmed and can be escorted to the Airlock to gain some weapon bonuses. Note that Panic Rooms
may occasionally contain a lurking Xenomorph rather than a scientist, resulting in a quick game over if you aren't careful. You may locate scientists thanks for the Motion Tracker: Scientists upgrade, or by looking for flashing green dots on a Security table.
Once a scientist is in the open, they will actively follow the nearest player, or run away from beasts and gunshots. They will open doors and turn off fences if any are in their way. If the Airlock door is in sight, they will run towards it on their own, after which you will gain one Science Point.
Science Points will increase your Re-Arm stat, which represents how fast you refill ammunition at an Armory. Gain enough Science Points and you will gain new ammo types (up to a 4th level), which give a slightly slower rate of fire but an overall increase in DPS.

• Do not waste time! Every second you waste not knowing where you're going, or activating sentries that aren't in a strategic spot, is a second you give to the game to spawn more beasts. Do not let the spawns get out of control, or what could have been an easy mission might take a turn for the worse.
  
• Be careful with Panic Rooms! There is a medium chance that a lab's Panic Room will contain a lurking Xenomorph and not a scientist. One quick way to find out is to fire a warning shot before opening the door. Scientists will scream - Xenos will not. Note that these doors also open during the Emergency Protocol, possibly unleashing a beast when you're not expecting it.
  
• Check your teammates' upgrades! Although not easy to do in the heat of the action, checking split screen (or simply asking teammates) can let you know what upgrades they have and whether they would be better off serving a specific role in the team. Someone with a Download Speed of 2-4 seconds could take care of sentries and datacores, while someone with Aim Assist and a good Motion Tracker could handle an area with breaches and no doors to lock them behind. At the end of the mission, if one of them has an Airlock pathfinder, they could lead the team to make sure no one loses valuable time taking wrong turns.
  
• Remember your Breaker locations! There is not a single map/pathfinder upgrade for breakers. In a pinch, you could use Infra-vision to guide you, as breakers emit more heat than the rest of the map, and they even emit a faint red light that you can see in the dark. But your best shot is simply to notice breakers and to remember where to find them before it becomes a necessity.
  
• Work as a team! Sometimes the game is just mean, and will generate a crossroads with several breaches that is near impossible to handle on your own, but also too hectic to handle as a team, due to the risk of friendly fire. Plan in advance with your mates (say one of you watches the left and the other watches the right) so that you may efficiently deal with the hardest rooms the game has to offer.

Feel free to recommend any new tips (or overall suggestions for the guide) in the comments!