There are only a few types of enemies on this game, each has at least two variants which only change their stats, every level features different variants.These enemies and variants are:

Variants

Normal: regular bots, you can beat them up with any weapon you want and they'll go down easily even with resistances, this enemy is the baseline for all the variants.

Crash Test: these enemies tanky, they resist a lot more elements than the normal ones so they'll take much longer if you don't have their weakness at hand

C.O.P: much like crash tests, these have a lot of resistances and will usually spawn with armor and ranged weapons, this category also has unique robots to level 2

Rusted: these enemies are faster than the regular ones, but they're really weak and go down faster, they're weak to fire and go down in seconds.

Scavenger: much like the rusted, they're very weak, but they attack insanely fast, these can be a tall hurdle for players who haven't learned to exploit dodge and attack windows yet. they're the main feature of level 2 and have one unique bot type. Their body parts are randomly picked from a pool when spawned so all scavengers look unique

Elite: much like the scavengers and rusted these are extremely strong and fast enemies, but they tend to go down faster than the others because they have less weaknesses, but they can be really intimidating.These are the main feature of the final level.

Flybots

Flying little pests that really like to attack when they're out of your peripheral vision. Much like every other enemy in this game they do not have sound cues for attacking, only visual, the "!!!" sprite above the enemy which shows up a few seconds before attacking.

They get specially annoying when they start spawning with face shields only a few minutes into the run, you can try to hit them in the back but it's not a guarantee because hitboxes in this game make no sense, just hit them in the shield two times and it should break, this will also push the flybot away from you to give you more room to breathe.

Small bots

Bots the size of the player character, they circle around the room and attack when they see you, they can carry a varied arsenal of weapons but they're not very threatening either way, these enemies teach the player to dodge and exploit windows for attacking

They can wield a lot of different weapons like staves and dual blades, but that doesn't change their attack patterns much, just their range and speed.

Big bots

Very tall and wide bots that take more hits to down, their arsenal is one of the most threatening in the game, but on their own they're really easy to dodge, if they have no weapons they'll slowly chase you and do a very slow dive.

These enemies can spawn with armor, and chainsaws, which is the deadliest combination in this game. Armor makes it so you have to hit the enemy several times to make the armor fall off before you can do damage, and gets punished and stunned for hitting the armor leaving you open for attacks, making armored robots a chore to deal with, hitting them in the back has shown success of dealing with the armor faster, but it still takes a few hits.

The chainsaw big bots is one of the most threatening enemies in the game, when they rev up their chainsaw they get super armor to all of your attacks and start running and tracking you, turning way too fast, there is not way to counter the chainsaw dash since it likes to go through shields at times because hitboxes make no sense on this game, so you have it wait it out and attack when it's over if you don't want to risk it going through your parry.

C.O.P big bots can have the other most annoying threat in the game which is chaingun arms, the proyectiles are fairly slow so they're easy to notice, but much like the chainsaw it's tough to get past the attack once it starts.

Mini bots

Small drones that go down very fast, and have very little means to defend themselves, they're the least threatening enemy in the game, but some of their support variants can be annoying at times.

They can spawn with shielding and healing powers to help other bots, so it's best to target the little bots first if they're in the room.

Spider bots

Very tall miniboss-type enemy, presented in certain rooms in level 1 as a challenge, but used more casually on level 2, tough but easily predictable.

They can spawn with a very easy to notice laser and rockets, which are not that difficult to beat, but don't get close to it for too long because it also has very fast melee attacks.

Worm bots

Featured solely on the level 2 sewer section, they can be really annoying if you don't have a fast weapon to counter attack them and force them off the ground.

Dog bots

Featured prominently on level 2 as C.O.P and scavenger dogs, they're very fast, and move around a lot, but don't offer much else new, their equipment can be really annoying as is all of the C.O.P equipment.

Other

There are other robots in this game such as some buildings like the C.O.P turrets and alarms, they only do one thing and don't attack back like the spider bot, so they're not as big of a threat as they may seem.

Level 1 is the only level on the game that has singposting and it's really easy to miss.

If you ever find a door with a red warning sing or a bunch of trashy green signs telling you to not go there, that means that's the path to the boss.

Every level in the game has two bosses but you'll only get to fight one every run.

B-DDS Knight

This guy might look very menacing but it's easier than it looks, it's also the second easiest to cheap out, sometimes it spawns with a rocket launcher, I don't know for sure what triggers this yet but you can destroy it if you hit it enough times.

Altough its attacks can reach very far it doesn't have any protection against airborne targets, if you have a weapon with a good plunging attack just spam it and this guy is done for, but don't forget to dodge.

Most of the time it's better to jump over its attacks instead of dodging, most attacks have a lot of horizontal reach but not vertical.

This guy also reacts very agressibly to elemental weapons, if you have a fire weapon it gets angry and starts attacking faster, and if you have an electric weapon it gets stunned temporally giving you time for a few extra hits.

FRANK-Y

This is the boss I had the most trouble with but once you get the attack patterns down it becomes really easy.

The fight is really straight forward, FRANK-Y attacks, you dodge it, then you get to choose between hitting its legs until it falls down and then pummel its face until it's dead, or just go for the face right away depending on your weapon, I personally recommend going for the legs if you have shorter ranged weapons.

Try to keep yourself at a safe distance so it's easier to know when the next attack is coming, being too close can be really dangerous.

Keep in mind you might not get it on just a few hits, on the release update FRANK-Y was buffed and its legs got armor plating that you have to break first.

Just like the first level, this level has 2 bosses but you only get to fight one every run.

Unfortunately this level has no signposting, it's easy to get lost, including the fact that there's a whole sub level underground, there's no real way to know where you should be going without a fully upgraded explorer's hat.

You'll enter through the sewers if you defeated FRANK-Y or through the surface if you defeated B-DDS Knight on level one.

In this level running away from enemies becomes a more viable tactic since scanvenger enemies are very fast and relentless, you'll probably have to fight them with underpowered weapons from level one but level two has plenty of gear for you to grab so you can defend yourself properly.

COPGORE

Found in the surface, this boss used to be a lot harder in the early access build, there was a really awkward camera angle and the boss had a tendency to destroy the only thing that could damage it.

It's very important to have a good weapon for this fight, COPGORE likes to spawn a lot of enemies and you really don't want to get swarmed by armored C.O.P. chaingunners.

You can't do damage directly to the boss, you have to wait until it decides to shoot a very obvious and big missile that moves very slow, hit it to deflect it back. Don't worry about the tether, the rocket avoids crashing into it naturally. (Apparently the tether was entirey removed from the game after I wrote this)

It takes about 4-5 cycles to beat depending on your luck.

Herbie

Found in the sewers, this big worm is by far the easiest boss in the game, It's recommended to have at least one speed upgrade for this fight since the arena is huge.

You can't hurt Herbie directly, you have to wait until it decides to stop chasing you and charges at you, then crashes into a wall, you'll have to enter through the very end of it's tail and start smashing the generators inside it, keep in mind that they explode and if you get hit by the explosion you might loose a few seconds. You can get up to 2 generators per cycle, but it's not necessary to hit them from the inside, you can also hit them from the outside if you feel like you have little time or you just feel like it (thanks to Ryouhiko)

Probably the hardest part about this fight is when Herbie starts circling around you forming a mini arena with enemies you have to fight to continue, however, the Herbie circle adjusts to your position so you're always on the center, you can run away from the enemies, make them touch Herbie and die so you don't have to fight them yourself.

Herbie is really really big, try to keep your distance away from it as much as you can.

There's not much strategy to this level in general, find the elevator, fight enemies, repeat, you might notice the lack of a minimap, you don't need it in this level, you can see your progress in the pause menu where the map should be.

There's only one boss on this level and it's the final one

Quality Assurance System

This fight can be a bit hard because you can only damage QuAsSy in a very specfic weak spot, the "face", it's got unbreakable armor, it'll sometimes open up this armor so you can land a hit, however, you can mess with the AI if you stay too close to the face constantly and brute force the cycle, vorpal weapons can hit through this armor making easy work of this boss.

QuAsSy attacks with lasers that extend to the walls, so it's recommended to have Heart's dodge and jump upgrade for this fight.

Since you have such a tiny attack window, the disco bomb can be really useful sice you get to do damage even if its lasers are up. (thanks to Soshidow)

*SPOILERS AHEAD* Do not continue if you don't want to get the good ending spoiled

If you finished Slash's quest line before getting to the final boss you'll get different dialog this time, it's completely impossible to hurt QuAsSy, Slash'll be constantly telling you to stop, to actually progress the fight you'll have to get close to Slash and open the upgrade menu, a new option to recycle yourself becomes available, use it to heal Slash.

Random facs that I've found while testing and analizing the game.

-In the early access builds, there were 2 extra slots for bosses in the enemy gallery that couldn't be found or killed, these were removed on the release build.

-COPGORE's fight is known for being the boss fight that got changed around the most during early access.

-Slash doesn't count as a boss since they are not an enemy in the first place.

-The game has two conflicting designs for QuAsSy, there's one for the dialog portrait wich is also the trading card art and a very different one that appears on the ending cutscene.

-B-DSS Knight's name is a pun on the word "badass knight" (or boss knight to some)

-Herbie's boss room is the only place in the game that features a semi destructible enviroment.

-COPGORE is both a Colonel and a Lieutenant.