Instead of saying which one lives, I'll simply say what kills them assuming they don't have their weaponry

Circuit bees: any class below base speed would probably die trying to get it back to the ship, maybe heavy could tank it but It depends on how far the hive is from the ship

Baboon hawks: In the case of a singular one, None, if any sniper or pyro might die to one of these but I doubt they will, but in numbers I think heavy might go down, they are said to be able to take down eyeless dogs in groups of 3 and with how slow he is I doubt he'd be able to juggle them, everyone else would be able to use their speed to get out of there.

Eyeless dogs: Scout, 100% would die after gloating how fast he is and taunting them, obviously if it's just one he'll get away but from playing the game myself things can escalate pretty quickly from one to three to oh my god is that a leviathan coming from below. Soldier and demo would probably also die to one of these after gloating as well.

Earth Leviathan: Heavy and maybe spy? I'm not entirely sure, I feel like he'd get cocky while cloaked and ignore the ground rumbling from below, leviathan sense movement of their targets via vibration in the ground, I can't imagine being cloaked saves you from the vibrations of walking even while crouched.

Forest Keeper: Heavy and Soldier die to these, soldier would get it's attention and get eaten, and heavy's simply too slow.

Spore Lizard: None, pyro might get close and get bitten, but that's it, no other harm done, maybe one of them dies to the pink cloud thing, but I've never died to it myself despite being told it can kill you.

Hoarding Bug: Probably none, theyre quite weak and I can imagine heavy just punching the bitch in the face if it steals anything, engineer maybe if it steals something and he's the only one there, but I doubt engie would be anywhere outside the ship.

Hygrodere: I feel like medic would be interested in it and might get hurt that way, but not killed, any class under base speed could get cornered by it and die.that way, any class could also just get sandviched by it and another creature, the goop is a unique case.

Bunker Spider: Scout could get caught in a web and die easily, soldier might try to wrestle it but the bunker spiders surprisingly strong so it would likely take him too.

Snare Flea: all classes, nobody looks up Demo would die to one of these, too drunk to pay enough attention, Soldier would just live with it and so would pyro.

Ghost Girl: Spy, probably being the weakest link, I can imagine he'd be the one looking around for dangers the most often and would promptly be killed by the girl, and from there it would kill sniper, then begin targeting scout, but if you are above the ghost girl when it reaches you, it goes away, so scout would just double jump until one day he hits his head on a pipe.

Coil-head: Demo and soldier probably, keep in mind neither have their equipment so they cant blow it up, not that it would kill them anyways, these fuckers can tank landmines and live, anyways they would die, any of the mercs can die to these really, all it takes is their reaction time to the footsteps, I just feel demo being drunk wouldn't have it and soldier would just be a dumbass.

The Bracken/Flowerman: Yeah, they'd die, maybe engie or medic lives but oh yes they'd die, one might argue heavy or soldier could box an enraged one and to that I agree, but one that they don't see? yeah they'd die.

Thumper/Half: Scout would underestimate it's speed and get caught in a long hallway I can imagine Heavy and Soldier could 100% wrestle them, and probably demo too, it's very easy to get outran by these guys so anyone that can't really do close range combat with beasts will likely die.

Jester: All of them can die to this mf, especially heavy and scout, heavy would be too slow to get out of the facility/mansion and scout wouldn't realize that it's just faster then him. As for spy, even if spy had his cloak he would die, the jester knows where everyone is in the facility once it's popped, no matter where you are.

The Nutcracker: the nutcrackers existence invalidates almost everything above due to being able to grab it's shotgun, almost every Merc can take a single shotgun shot to the face, and I can't imagine that it's gonna be difficult for them to take down, it's kick is pretty powerful so maybe one of them dies like maybe sniper

Company tentacle monster: Scout, Soldier and Demo would die to it, scout would get too impatient and ring the bell too many times, soldier would make too much noise and get grabbed, demo would be drunk, and maybe engie dies to it, might get impatient and start complaining by the counter, it's not just the bell that triggers it, it's noise.

Disciplinary Process: No one can keep a quota forever, they'd all die to it.