Although not technically an Evolution upgrade, the Loop Selector upgrade choices when you complete an S2 run work in a similar fashion - you pick one of two such upgrades - so I added a Loop Selector section to this guide.
NOTES: The Loop floors are absolutely brutal in difficulty, so boosted health regeneration sounds like a good idea, although I guarantee you'll take such a pounding from Loop level enemies, that health regen won't do you much good. :)
NOTES: If you completed a Synthetik 2 run, it's unlikely you relied on your sidearm very much. I'm not inclined to recommend this unless for limited-ammo or other reasons, you tend to rely on a sidearm more than your main weapon(s); or if you're just determined to play S2 to bloody end with just a pistol. :)
NOTES: Going out on a limb (joke), I'll advise that if you love to spam your class' Mobility hotkey over and over, then this Loop Selector upgrade giving a decent (30%) chance for using that to not trigger cooldown (i.e., not be "consumed") is a nice thing.
NOTES: To restate the obvious, if you rely heavily on items - especially summoned friendly units - then the ability to use them much more often is a great choice.
NOTES: This niche upgrade is for players who are constantly firing while moving, which to be fair, is something you have to do on the Loop Levels because of the sheer volume and greater aggressiveness of ALL enemies.
NOTES: Probably only of interest if you concluded your run with at least one disappointing main weapon that you'd like to try replacing.
Divine Shield
NOTES: Highly recommend this shield boost because you'll take a severe blasting from all the much nastier enemies on loop levels.

NOTES: Good pick if you like the idea of using Breacher's dash ability as a direct physical damage attack and if you already chose Power Kick ability.

Maybe not the ideal pick if you're focusing more on tossing charges and ranged attacks, and didn't choose Power Kick.
NOTES: If you tend to ride on the Ragged Edge of HP Disaster, this Evolution upgrade is for you. :)
NOTES: If you like to throw Breaching Charges frequently, this is a no-brainer.

In my experience, the Lightning Clusters seem to blink and remain in effect either indefinitely or at least for a long period of time.

They don't appear to inflict any friendly fire on your character or your summoned friendly units.
NOTES: Good choice if you're using Shoulder Dash frequently to charge into the middle of groups.

Not so useful if you're just using the dash more for evasion or to get somewhere faster.
NOTES: Good synergy with the Breaching Charge ability because you can dash into enemies and STUN them first, making them a sitting duck for a Breaching Charge and/or melee attack.

NOTES: This one's useful if you're keen on items that summon friendly units or turrets. Obviously, if you're not keen on this or you don't have any at the time you run into this, you might choose something else.
NOTES: The "self knock back" means this may help put some distance between you and enemies that got too close, but note if your back is already against the wall, that won't really help. :-)
NOTES: Although I don't play this class much, losing this high a percentage of weapon damage seemed to reduce my effectiveness, and I wasn't sure the faster cooldowns - which seem akin to the Brawndo beverage item's effects - was really worth the tradeoff.
NOTES: Good choice if you like to Telefrag (teleport) as often as possible.

And don't forget that you can teleport through walls and even across gaps in the floor. :)
NOTES: Although I tried this upgrade, I found it difficult to perceive it was doing anything during the chaos of combat.

NOTES: To state the obvious, if you like to send your Commando dashing through enemies often, this is a good pick.

If dashing through enemies frequently is NOT your thing, give this a pass.
NOTES: A fine choice for Commandos who love to dash through enemies. :) Grab this and Full Reset below, and you become a dashing dancer Commando.
NOTES: Obviously, if you like to slash, slash, slash, pick this one. :) The reduced cooldown in particular will let you slash enemies much more often.
NOTES: I've picked this several times, and Particle Cloud has never done anything during gameplay.

I think it's broken?
NOTES: I like this one. Although I don't know what the % chance is for the plasma shots to trigger, they seem to fire off often enough to be useful.

My usual "duh" observation is if you're more into your commando shooting than dashing, this is a top pick. If you're more into dashing/slashing, watch for picks like Hyperblade, Full Reset and Commando Weapon Mastery as outlined above.
NOTES: If your Commando is constantly gasping for ammo, this is a good choice.
NOTES: Another good choice for the slasher commando.

NOTES: This powerful upgrade to the Rocket Run / Rocket Boost Class Movement Ability adds more impact, but more importantly damages enemies along the ability's path.
NOTES: Advantage of this over "explosive ammo crate" is you don't have to stand in radius to use this. Just pick up some ammo, to get 15 explosive shots to fire.
NOTES: If you're all about kabooming enemies on screen as often as possible, this is the right upgrade for you. :)
NOTES: I found Grenadier underwhelming because I rarely have time in combat to point my character in a certain direction when reloading, and so often my grenades didn't impact any enemies.

NOTES: Another must-have for Demolishers seeking to kaboom everything on screen, as often as possible.

NOTES: For the Eraser shot fan.
NOTES: Although this sounded fun/useful, in my lone run with it in place, I never noticed a distractor drone ever deploying at all. I'll re-check my gameplay video to see if I missed it.

For now, I've reported it at forums as possible bug.
NOTES: The quick reload and firing rate buff make this very powerful in combat, although with certain small-magazine weapons, the firing rate buff may chew up your magazine faster than you may like.
NOTES: Although this is a straightforward damage buff, I've had difficulty telling if it made much difference in combat.
NOTES: Useful if your Eliminator is sporting a bronco-bucking machine gun or SMG, but it may not be so useful with most other types of weapons.
NOTES: No-brainer choice if you rely heavily on the Distractor Drone, as most Elminator players do.

This is especially helpful against melee-enemies who tend to run up on top of Distractor Drone and have no ranged attack pew-pews that the drone can reflect back at them.
NOTES: The "duh" tip is to remember to Roll to trigger this auto-firing of two lasers.
NOTES: If your goal's to spam your Eliminator's abilities buttons as often and as quickly as possible, then get on this boat and ride it. :)

https://youtu.be/U52ZmhH3OJw?si=Rwg1NMjZsc83A64E
NOTES: The Ammo Supply Spider periodically appears, and you need to be within its radius - marked on the floor - to gain its benefits. It's not very mobile, and doesn't seem to move around to preserve itself.

On the PLUS side, you often will have MULTIPLE Ammo Supply Spiders roaming a level, these are very tough (high HP) and can effectively serve as decoys that soak up a lot of enemy attacks that would otherwise be directed at you.

Also, even when the Ammo Supply Spider's "ammo radius circle" is NOT visible, your Heavy Gunner will still get an auto-reload when it moves near the spider.

The problem is you have no control over when these spiders appear, where they move (they'll follow you, slowly), and in boss fights where it could help, it may not appear at all.
NOTES: This one seems most useful with weapons with extremely large overall ammo capacities. When you Active Reload, your weapon will then continously draw ammo DIRECTLY from your weapon's "overall ammo capacity" and ignore your weapon magazine's far more limited capacity. So this enables you to fire continuously for a longer, without needing to reload.

However, if your favorite weapon(s) has limited overall ammo capacity, this is probably NOT the choice to go with.
NOTES: I didn't see a 10% chance as occurring often enough to bother with this upgrade.
NOTES: To me this is like the Class Evolution upgrades that trigger when you reload. It's not always a given that you'll want to eject or reload a weapon when near enemies.

So think about that when pondering this type of upgrade.
NOTES: Although this choice gives you a bevy (5) of weapon upgrade kits and doubles weapon attachment power, it comes at a steep cost in item power.

So to state the obvious, if you're heavily relying on powerful items during a run, this might not be your pick. If you don't lean on items and are hungry for weapon upgrade kits, then your ship has arrived. :)
https://youtu.be/CknyM9NZFlo?si=3fTG59bo7izo1Fi1
NOTES: This auto-deployed turret - when you use your Class Specializtion Ability - can *only* fire in a straight line. Although this mean it won't h it much, much of the time, it does deplay fairly often and if nothing else, it helps draw attention from you.

So if you have no summoning-type items, at least this Class Evolution upgrade can drop this turret on occasion as a decoy.

It can be useful when pointed at a narrow passageway, but even if you try to use your Class Specialization Ability at the right moment, it may not point in the correct direction to be useful
https://youtu.be/OwzaFSgaPxI?si=j9iK0WeKs0Mgcmjf
NOTES: JULY 2025 - update. This class evolution pick now WORKS, and is very effective.

It basically sprays gunfire 360-degrees for about 7 seconds before detonating with a small explosion. It can be helpful in keeping you or a co-op group from getting overwhelmed and also saving some ammo.

The popcorn box deploys at the start of a level and thereafter whenever you start a new battle and this isn't on cooldown period, it should deploy.

Just keep in mind on some maps, you may just run from one fight to the next without any real intermission between, which may be when Popcorn Box resets to become available again.
NOTES: The Heavy Gunner class is extremely slow when equipping a machine gun, so the main appeal of this Class Evolution upgrade is in the form of buffs to movement speed and dodge chance. Useful if you want your Heavy Gunner to be more spry, especially in co-op, where you might struggle to keep up with fellow players.
NOTES: Useful if you want your Heavy Gunner to spew rapid-fire lead as quickly as possible, although some smaller magazine machine guns might empty too fast, even with the increased ammo regeneration.

NOTES: If you're running into low-ammo issues, this Class Evolution pick can help a bit.

I'm not sure what the "1 extra magazine size" per summons means for the tracked Hunter drone. I guess it means it can fire its weapon slightly longer before needing to reload?
NOTES: This Class Evolution pick offers outstanding buffs at the start of any combat engagements.

Note that the firing-rate buff could empty out small-magazine weapons quickly.
NOTES: Captain Obvious says that if you rely heavily on the powerful Machine Hunter HEAT or HVAP shot ability, then having a second shot when you use the ability will be your jam.
NOTES: This might be a better fit for semi-automatic weapons and sniper rifles, where you have a second to realize you've got these five special rounds to play with.

Maybe not so much best fit with fully automatic weapons, with which you might accidentally chew through the five MAG-L rounds before you even knew you had them. :)
NOTES: As what seems to be the only Machine Hunter Class Evolution upgrade that adds some welcome - albeit slow - health regeneration, this was a keeper for me. It will basically heal your Machine Hunter a little bit every time you activate Turtle Mode.

That's because Machine Hunter's precious Snappy tracked drone eats up the utility slot, giving the class no direct-healing abilities.
NOTES: Vehicle Stopper can help prevent you from getting overwhelmed by hordes of fast enemies, especially on levels like the Data Center and the snow base.

I do find the constant "blinking" animation of the Vehicle Stopper tracks getting laid to be a bit distracting.
NOTES: This didn't appeal to me in part because I feel like rarely in S2 do I have the luxury of my character standing still for any period of time. Your mileage may vary. :)

NOTES: I didn't originally find this appealing because my Recon can rarely afford the luxury of standing in place during combat. However, it seems like now it just triggers on engaging in combat, and it no longer requires standing in place.

HISTORICAL NOTE: This evolution upgrade was originally called "Weakpoint Scan".

NOTES: For Recon Sniper, mobility means using Critical Disengage or Reposition. So those will trigger this class evolution upgrade, dropping a mine and partially reloading your equipped weapon.
NOTES: If you pick this, you'll regularly see a large, colorful glowing radius on the ground delineating the area in which you'll want to stand to gain Defense Perimeter's bonuses.

Seems like the color varies? I've seen orange, and I've seen blue, although I may be confusing it with an enemy's debuff ability's visual effects.
NOTES: Just note this is meant for fast-firing weapons, so it's not so useful on sniper rifles and most handguns (except the full-automatic models).
NOTES: I chose this one because a slightly slower-firing sniper rifle doesn't seem to bad a drawback for the nice critical damage and base damage benefits provided.
NOTES: Ran into this one after completing S.A.T. Academy floors and the dual sawblade flying saucers boss.

Nice buffs when enemies are near you, although bear in mind if you're mostly using sluggish firing sniper and/or semi-automatic rifles, faster firing buff will only do so much.
NOTES To state the obvious, great for fans of all pistols in S2, and if you're frequently gassed on ammo and resorting to your sidearm a lot.
NOTES: Although I went for this one, I found it difficult to discern visually if anything beneficial was actually happening in combat.

NOTES: The way to go if you love to rush your Riotguard into the middle of crowds, giving Impact Charge more punch and impacting enemies along the route of your charge - and not just at the final destination.
https://youtu.be/cwXHB3UFGUc?si=WjZ8TgXSojMsUSu9
NOTES: This powerful Class Evolution upgrade provides you an ITEM, which when you activate it, causes your Riotguard to kneel - rendering your character immobile for a couple seconds while firing the rounds - and blast off four fiery, heavy-damage rounds, and briefly enjoy a 100% dodge chance while kneeling.

Finally tried this in July 2025, and it is very awesome, especially against the Radar Dishes that call in those annoying beam attacks and against turrets and transmitters. Good against all enemies too, just you have to weight it against becoming immobile for a couple seconds while firing the rounds, even if you get a big dodge boost.

You just have to weight it against not being able to use a traditional item in the item slot occupied by Hot Shots.

P.S. For those sensitive about naughty language :-), using Hot Shots causes your character to yell "BULLSH*T!" every time. I found it hilarious the first few times, a bit tiresome after that. Your mileage will vary. :)
NOTES: Fine choice if you like to wade in and shield-bash a lot.
NOTES: Interesting upgrade that triggers ranged weapon buffs that are based on using your Riotguard's shield.
NOTES: Good pick if you like to have your Riotguard wade in regularly at melee range.

You'll hear a sound effect indicating the static build-up and see an electrical aura when it triggers.
https://youtu.be/bzNGrSNY_uo?si=6FSOLC-FAimhA5k-
NOTES: This powerful Class Evolution upgrade is one of my favorites in the game, as it spawns multiple, heavily-armed bikes to fight by your side. However, it doesn't seem like they spawn very often. In my experience, they'll usually spawn at the start of a floor/map, but then you may not see them again on that floor/map.

Do note that they are fragile and extremely aggressive. They may take a boss or tough enemy out in record time, but they also may "aggro" an entire map to come after you. You also have no manual control over when they deploy. I think they just appear when you're in combat, and if the cooldown period isn't in effect.

Also, on some maps, the bikes spawn in a map corner and won't leave to go after enemies until you "kite" some enemies to them to get them to start combat.
NOTES: Will help improve your Riotguard's chances against big-fish Elite enemies, and the increased stun chance means taking less damage.
NOTES: This Class Evolution passive is sort of a leftover from the abandoned Riotguard variant, in earlier Synthetik 2 builds, that could shoot out electrical blasts.