To understand anything about the mech chassis, it is absolutely required to understand what the numbers mean in the game. So before we talk about how the chassis are different, let's take a look at what means what.

When you select a mech in the production bay, the game will show you a list of mech stats in the middle of the screen:

• Arms: not listed in this view. Arms allow digging through terrain and melee combat. Melee combat ability can cut/rip Fragellum tentacles! Only two mechs in the game have arms.
  
• Weight: Primary stat for "zippyness". More mass = difficult to accelerate = difficult to dodge. Note that bigger mechs require more armor plates than smaller mechs to cover the surface, resulting in additional weight gain from armor for bigger mechs.
  
• Passive armor, flat: Each mech can only use 2 layers of standard armor plating (or up to 4 layers of compact armor plating, which can be researched). Each mech can put on one layer of armor coating on top. Every bit of armor that the chassis brings is free. That means it doesn't spend the valuable armor plating slots, doesn't put weight onto your motors, and doesn't need to be produced. Armor is a flat damage reduction AND acts as armor hitpoints (armor can be chipped away during combat).
  
• Heat / impact / water current resistance, in %: Reduces how much external AND internal effects affect you. 50 resistance = half the effect. Note that drilling through terrain causes impact to the mech, and the recoil from firing weapons does as well. I think heat resistance is both from internal and external sources (didn't test this one).
  
• Speed, multiplier: Maximum speed of the mech; it's what you expect. Unused weight = more speed. More motors = higher maximum weight, but also more weight, which results in higher top speed but reduced zippyness.
  
• Reload time, in seconds: How long it needs to reload, in seconds. The actual reload during combat also depends on weapon system (different weapons have different reload times). More on that later. The overall reload time is modified by the control stat of the mech, in percent. 30 control = 30% reload time reduction.
  
• Fire time, in seconds: How long the mech can shoot before it needs to reload, in seconds. All kinetic weapons will use kinetic ammo. The more weapons you have, the less shooting you can do before you need to reload. The ammo stat of the mech (see AUX modules) adds fire time, in seconds. So 6x ammo AUX = +6 seconds fire time and -30% reload time.
  
• Weapon and AUX hard points: how many weapons / auxilliary modules the chassis can equip. More hard points = more versatility and (most of the time) more firepower, depending on how you set up your weapons. Note that the "underwater mechs" have only 2 AUX slots, so most people avoid them. Why this is a mistake, you'll learn in the next chapters.

The values you see there are the mech's base stats. In general, base values have more significant effects than modifiers.
Base value > modifier. Remember that, it is important for chapter 4.

Modifications can be absolute, or relative. For example the ammo AUX adds an absolute 1 second to the base fire time, and also adds 5 control. Control is a relative modifier on the reload time, so this also reduces the reload time by 5%.
Additional modifiers can be added (additive, NOT multiplicative), and the modifiers are applied to the base stats.

Example 1: 6x ammo AUX results in +6 seconds of firing time, and 6x5 control = -30% on reload time. Together with a 50 control cabin, this means you can get to a 80% reload time reduction, which is applied to the BASE reload value.
We will come back to this when we compare mech chassis down below.

Example 2:
The dodge value of a mech is how many melee attacks it dodges, in % (90% is the maximum, 75% from the mech and an additional 15% from pilot skill). You can check it out in the engineering bay, in the weight menu:
As you can see, an empty starter mech already has >60% dodge. This is significantly modified by the current mass of the mech. Add a simple reactor and see how the dodge rate is halved immediately, down to 32%. The AUX module for +25% dodge is applied to the dodge base value. So +25% on a high dodge base value will be more effective than a +25% bonus on a low dodge base value.
Since the weight directly changes the dodge base value, it has a massive effect on the final dodge value, both directly and indirectly by defining how effective a dodge AUX is.

To understand the impact of the mech stats, you need to understand what each number effects, and whether it is an absolute effect or a relative one.

Let's take the two first mechs as an example to understand how the numbers interact with each other. For the sake of simplicity I'll call the starter mech MINER.


As you see, the PLATE is significantly more expensive in terms of resources, roughly 2.5 as costly. But of course the amount of mechs you can bring to a mission is limited, so let's take a look at what you get for the investment.

• Weight and speed: 5 tons difference. When you add all the modules it can equip (+2 motors, +1 weapon), those 5 tons will not matter anymore. In fact, since the PLATE can equip more things, it'll probably end up weighting more than MINER, so it will be less dodgy. Together with the significantly lower base speed, this already gives you a hint on what archetypes these two might be. One is more of a skirmisher, the other one more of a fighter.
  
• Resistances: PLATE has slightly higher heat resistance (15% vs. 20%), which can be relevant when operating near thermal tipping points, but is probably not a deciding factor. However, impact and water resistances clearly show the mech preferences. PLATE does not like being under water, but is drastically more stable and can't be pushed around easily. Combined with the speed profiles, you start to get a good feeling for what the mechs prefer.
  
• Weapon firing: Now this is where it gets interesting. Look at these numbers: firing time is up by 1, reload time is down by 1. And this is where we come back to the whole base stats vs. modifier thing. You may think "Yeah whaterver, 1 point difference is negligible. But think again!
  From MINER to PLATE, this +1 firing time means a +33% firing time upgrade, and the -1 reload time actually means a -25% reload time upgrade. This is HUGE. It fires significantly longer AND reloads significantly faster!
  
• Other: Some of the stats can't be seen in the production screen, so it's always worth checking out the prototype that you get from researching the chassis. In this case, the PLATE doesn't have any arms, but can equip an additional weapon and 2 additional motors, meaning you can put alot more/heavier stuff into it. Considering how the weapons configuration works, this means you can put less into weight reduction and more into damage - the PLATE can handle the higher weight.

So with these 4 aspects taken into account: speed, resistances, firing, and "hidden stuff",
you can get a good impression of which archetypes might work especially well on a certain chassis.
MINER is quick, versatile, and cheap.
PLATE on the other hand is much better at shooting, but more of a slow "hold your ground" mech.

This is your starter mech. The chassis was used for asteroid mining, back in the good old days when Earth wasn't infested with Bugs. Nothing to compare to, at the beginning.
MINER is the most versatile mech. It can do pretty much anything and will never disappoint you.

Throughout the game you will notice that in fact it excels at a few things, where the other chassis are more limited. Most noteworthy of those are the existence of arms and legs. Might sound silly to you, but it's actually an issue with all the other mech chassis.
Noteworthy specialties:

• MINER is one of only two mechs in the game that has arms, and thus can drill through terrain and fight in melee. Both are quite useful. Digging allows you to carve advantageous paths, reducing your dependency on terrain. And melee is quite effective against your standard Operarius swarm and can save you when you get swarmed. It can cut/rip Fragellum tentacles as well, so it can free itself (and maybe allies?) whithout the need to kill the Fragellum, which might be shielded by lots of bugs that eat all your ammo. It's a backup weapon, but an effective one (check the ingame manual for more detail).
  
• MINER is fast. In fact it's the fastest mech in the game. And quick positioning is valuable in many situations.
  
• MINER is cheap and quick to produce. It becomes even cheaper if you finish repairing the mech hangar district, which will allow you to produce up to 10 of them at one. This makes it the only realistic candidate for a self-destruct system later on.
  
• MINER has decent water movement. It will be able to handle underwater missions well enough, although specialized mechs will be significantly better.
  
• MINER can only field up to 2 weapons. This means a couple things. In terms of shooting it will probably focus on a single task/role. The versatility comes from having 6 AUX modules, which pretty much means it can take any fighting role you want it to take, plus several utility roles if you want to, or one extremely well done utility (you ABSOLUTELY can put several repair drones or missile defence systems on it).
  2 weapon mounts also means it is the only mech that can be fielded with only one weapon. Why you would want that? Well, less weapons = less cost to send people on missions = better resource efficiency. And some weapons and weapon setups are so heavy and/or hard hitting that you don't want or need more than one or maybe two of them.

Area of expertise: versatility, utility, speed
Preferred archetypes: Versatile Skirmisher / Supporter / Melee

PLATE is the first mech you can unlock. It has been a popular combat mech throughout history and brings significantly more firepower than the MINER, at the cost of mobility.
Noteworthy specialties, compared to MINER:

• PLATE has no arms, so no digging and no melee.
  
• PLATE has +33% ammo capacity (fire time), -25% reload time, and an additional weapon mount. It comes with 2 extra motors to carry the extra weaponry and allow for more armour. Less points needed in weight reduction (see weapon configuration) means more points in other weapon stats like damage or precision. So overall it packs a significantly bigger punch than MINER.
  
• PLATE will not be pushed around easily, neither by internal force, nor by external force. It is significantly slower than MINER, has less dodge, but decent impact resistance. So it is less mobile, but more stable.
  
• PLATE can bring as much utility as MINER, due to the 6 AUX slots. You might want to emphasize buffing your weaponry, though, since any modification of weaponry will be more effective due to better base stats, and any modification of mobility will be less effective.
  
• PLATE does NOT like water. It will be even slower, and water currents will carry it away easily, unless you put significant effort to compensate via AUX slots.

Area of expertise: firing weapons, utility, setting up and holding firing lines
Preferred archetypes: Versatile Fighter / Support

This is your first dedicated underwater mech. It has been developed for under water exploration and was modified for combat encounters. The HOLO can move swiftly under water and brings quite a bit of firepower, even on land. That comes at the cost of reduced heat efficiency and versatility. It has no arms and only 2 AUX slots, which can easily be mistaken as being weak.
Noteworthy specialties, compared to MINER:

• HOLO has no arms, so no digging and no melee.
  
• HOLO has +33% ammo (fire time), and a whopping -50% reload time! While all weapons profit from this, it is especially useful for weapons with inherently long reload times, like rockets and missiles. It comes with 2 additional weapon mounts, and 2 additional motors to carry the extra weight. So overall it can pack an even bigger punch than PLATE.
  
• HOLO and PLATE have the same movement speed, but HOLO has higher impact resistance and is immune to under water shenanigans, so will not be affected by the drastic speed reduction.
  
• HOLO comes with +5 armour, which is a free armor plating that doesn't require an armor plating slot (each mech has 2/4 of those depending on research, plus an armor coating), despite being 10 tons lighter. That makes it the tankiest armored mech on the field.
  
• HOLO is vulnerable to heat. I recommend taking some extra time to test thermal behavior in advance. Due to the lack of AUX slots, you need to engineer your reactor and your weapons accordingly. The fission reactor can be set up as a giant heat sink while still giving more energy than the combustion engine.
  
• HOLO has only 2 AUX slots. Many people easily judge that as being underwhelming. But take a closer look and see what you get for those -4 AUX slots:
  - 50% reload reduction (you can't even build that with 6 AUX slots), including half the heat from reloading of course,
  - an additional free armor plating AND a 10 ton weight reduction,
  - even higher impact resist than PLATE,
  - and immunity to water movement issues (water resist AUX gives +15 resist).
  You can NEVER build all those things with 4 AUX modules, not even close. But of course with AUX modules you can decide which bonuses you get, while these ones are fixed.
  
• Due to lower weight and free armor, it might be a decent duellist (high dodge while still wielding significant firepower and protection).

Area of expertise: firing weapons, cold environments, setting up and holding firing lines
Preferred archetypes: Brawler / Gunslinger / Duellist

QUADRO is a modern combat mech. It loses some of the PLATEs versatility to pack more firepower. It only brings a minimalistic reload mechanism, in favour of ALOT of space for ammo and special legs, weighing down the mech significantly. It has been developed to heavily fortify key positions.

Noteworthy specialties, compared to MINER:

• QUADRO has no arms, so no digging and no melee. It has special legs that are slow but can anchor to the ground.
  
• QUADRO has a ridiculous ammo storage (+166% fire time). This was possible by throwing out every screw and panel of the reloading mechanism that isn't strictly required (+100% reload time). That makes it especially useful for weapons that don't need to reload often.
  
• QUADRO also has a ridiculous amount of weapon mounts (+6), making the mech quite viable for a mix of different weapon systems to be able to handle anything you want it to. Just like the other fighters, it brings the much needed +2 motors to handle the extra weight from the additional weaponry.
  
• QUADRO is slow. It has very low base speed. It has special legs, though. They can anchor the mech to the ground, making it immune to any involuntary movement. These legs also help with moving through water and give the chassis decent water capabilities.
  
• QUADRO is slightly vulnerable to heat. Like the HOLO it has no heat restsance to speak of, but can compensate via use of AUX slots.
  
• QUADRO has a solid 4 AUX slots. That allows you to field it anywhere you want. Alternatively you can narrow down the biome versatility and focus on improving the already impressive weaponry even further. Any AUX that goes into the weapon performance will affect up to 8 weapons.

Area of expertise: firing ALL the guns!, holding key positions
Preferred archetypes: Weapon Platform / Overwatch / Artillery

TRIANGLE is a popular general purpose combat mech and can be seen as the big brother of MINER. It trades some of the versatility for slightly better defence and additional weapon mounts. The leg actuators have been switched to favour stability over speed and can compensate involuntary movement reliably. Thanks to using mostly standardized and efficient components, the mech weighs only 48 tons.

Noteworthy specialties, compared to MINER:

• At 48 tons it is the lightest mech, which results in the best dodging potential of all chassis, while still being the second fastest mech. It doesn't have arms, though :( but plenty of weaponry to stick into bug faces.
  
• TRIANGLE has several slightly improved combat stats: +66% ammo (fire time), +2 weapon mounts, and +3 armor. Be aware that it does NOT get the additional motors that the other fighters get!
  
• TRIANGLE has a solid 5 AUX slots. If you don't care for the speed, digging and melee of the MINER, but still want a versatile allrounder with excellent movement reliability, this a good choice. Due to most of the components being fairly standard, it only takes 4 days to build.
  
• TRIANGLE fills a role similar to the PLATE, but favors ammo over reload, and stability over carrying capacity. That makes it a middle ground between MINER and QUADRO. If you want the QUADROs stability but don't like its low speed and don't require that many weapon mounts, this is an alternative.
  
• The high speed and reliability allow it to dodge storms and comets and make it an excellent desert fighter.
  
• Due to the unique combination of characteristics, this mech might be a competent duellist. It is the second fastest mech and can have maximum dodge (75% for the mech, plus 15% pilot skill) while fielding more weaponry and more armor than the MINER. So you could dance with the swarm, probably with Aries, and maybe even Gammarus, while sticking close range lightweight weapons into their faces.

Area of expertise: utility, setting up and holding firing lines
Preferred archetypes: Versatile Fighter / Support / Duellist

Originally designed to repair space stations, TENTACLE has been modified several times to be able to serve as a combat mech. Due to its special 6/8-arm-design and the absence of conventional legs, this chassis is more flimsy than all others. It can't carry much, and it moves slowly. The torso is not big enough to hold much ammo, so the engineers focused on a highly efficient reload mechanism instead. The lack of space means that it has to rely on efficient electric engines to carry heavy weaponry.

Noteworthy specialties, compared to MINER:

• TENTACLE is the only other mech besides MINER that has arms to dig through terrain and do melee combat or cut Fragellum tentacles. It has more arms, which weight more. I assume it can handle more melee enemies simultaneously (not tested).
  
• TENTACLE has only slightly more ammo (+16% fire time), but the many arms allow it to handle 6 weapons with a ridiculously low reload time of 1 second (-75%). A high control cabin, the commander reload skill and the kinetic reload program can increase the reload speed even further, to a point where it stops being an issue - even for configurations that normally would have unbearably long reloads, like barrage missile systems.
  
• Due to the lack of space, TENTACLE requires electric engines to carry heavy weights, preferably highly efficient ones. It can only equip 3 motors.
  
• Excellent sealings make it a capable under water specialist, but can be used on land as well.
  
• TENTACLE is vulnerable to heat, but has slightly better insulation than HOLO. Due to the lack of AUX slots, you need to engineer your reactor and your weapons accordingly. The fission reactor can be set up as a giant heat sink while still giving more energy than the combustion engine.
  
• Just like HOLO, it has only 2 AUX slots. And just like HOLO, people tend to think of it as underwhelming because of that. But what the HOLO can do efficiently, the TENTACLE can do even better. It fields even more weapons and has basically non-existant reload, so it is an excellent gunslinger, provided you can balance the weight requirements to field the guns. It is the only mech that can field normal weaponry with 0.5 second reloads, and the only mech that can use map-deleting barrage missile systems with only 15 seconds of reload.
  Some people claim that the TENTACLE can bring so much DAKKA that you will struggle to see enemies amongst all the bullets and explosions. That being said, it does require advanced engineering skills to balance all the quite specific characteristics of the mech.
  
• Due to the mostly civillian parts and standardized utility limbs, production is as cheap and almost as quick as the MINER. Setting up the complex arm maneuvering and high end reload system still requires 5 production slots, though.

Area of expertise: unlimited DAKKA, cold environments, setting up and holding firing lines
Preferred archetypes: God Gunslinger / Specialist Fighter / Melee

CASTLE is pretty much what the name suggests. It brings excellent defence, as well as ridiculous offensive capabilities. Both are weighing down and slowing down the mech significantly. Even with additional motors it struggles to keep itself moving. But on the bright side, everything else also struggles to move it.

Noteworthy specialties, compared to MINER:

• CASTLE has no arms, so no digging and no melee. The 4 gigantic legs are completely built for carrying capacity and stability.
  
• CASTLE fields +10 weapon mounts, +366% ammo space (fire time), while using the same stripped-down reloading mechanism that the QUADRO uses (+100% reload time). It is questionable whether the +2 motors can handle all those weapons.
  
• It brings a decent +3 armor, immunity to invluntary movement both on land and under water, as well as improved heat resistance.
  
• CASTLE is slow. As slow as the QUADRO, just with more stuff in it, so probably even slower.
  
• CASTLE is not vulnerable to anything. Buf if you plan to dodge something, don't bother.
  
• CASTLE has a solid 4 AUX slots. Much like the QUADRO, that allows you to field it anywhere you want, but any AUX that goes into the weapon performance will affect up to 12 weapons.
  
• The design requires 10 times the resources and 3.5 times the time to build. At this point you just build it because you can.

Area of expertise: firing ALL the guns!, holding key positions
Preferred archetypes: Weapon Platform / Overwatch / Artillery

I recommend fielding a mix of both - main combat mechs for firepower and support mechs to protect the less versatile main fighters. The following list highlights where the different chassis have their peak potential performance.

HOLO: best allround fighter, under water specialist
QUADRO: best weapon platform
TENTACLE: best gunslinger, under water specialist
CASTLE: for when you just need the biggest meanest thing and don't care about time or resources.

MINER: best skirmisher, best digger
PLATE: best heavy weight shooting support
TRIANGLE: best light weight shooting support, best duellist

Due to the freedom you have in engineering your own mech versions, there are no/few hard limitations. Experiment, and come up with your own ideas! This is Mech Engineer after all :)

Example: I had a MINER specifically designed to be a hard hitting sniper and not much of a support at all. It was one of my main combat mechs in the late game and was quite vulnerable to widespread swarms, if catched off guard. But it also packed a hefty punch with drastically tweaked double railguns and had the speed to move into and out of key positions, to strike key targets, while the others defended a more advantageous position and provided a safe area to return to. It had melee weapons and a few AUX modules to protect itself while moving in and out, but was otherwise built for speed, range and damage.
This "starter mech" was one of the most fun things I have ever built. It was my little ninja sniper, and I took it into every mission I could, just because I had so much fun with it :D

Simplified and compared to MINER. Weight management means how easy (+) or difficult (-) it is to manage the weight if the mech is fully equipped.




I have probably missed some of the relevant stats. The mechs have many more attributes than the ones shown in the production screen. It's just really inconvenient to compare them in the game, because they are spread over multiple screens and windows.

If you spot something that you think should be mentioned, please let me know.
Keep playing around in the mechlab and see what you can come up with! Also, post your nifty little specialist builds in the comments, to share the engineering ideas and widen people's horizon on what they deemed impossible :)