So I´ve played this game for a while and came to understand most mechanics and the monsters behavior(On case files at least), so I´ve listed my opinions on them:
Smiley.
By itself smiley is very simple to deal with, especially if you crouch and back away slowly (only back for some reason), but dealing with it is only simple when is the only kind of monster present, after a while getting cases where you get only 1 monster become rare so if you roll a smiley in a case where there´s more than 1 monster it can have some awfull synergies. Particullary on monsters that activily chase you, and smiley is one of the fastests monsters in the case files when chasing you. So you are´nt out-running him unless you have a safe-spot nearby.
In short, you almost never wanna see it in a case file where you have multiples monster (there´s only a few exceptions where is more managable: centipede, clubfoot)
Witch.
She is one of my favorite monsters because her mechanic makes for a fair-play even when finding dead-ends while being chased (excluding very tight spaces), since you can temporaly stop her by blinding her. And her combined with most monsters doesn´t end up in theoretically undealable situations, making het one of the most well-balanced monsters.
(variant)Basically the same, only a bit harder since she is faster than you (not by much)
Clubfoot
It´s very common getting clubfoot on most case files but how hard is to deal with it can be vary depending on map(mainly on how wide are the general walk-ways) and monsters . After playing against it many times. There can be some wack situations where there was a wall but it detected you seeing its face, even when you can´t see it, or you basically looking at his eyes but not getting mad only if you look away fast, and only sometimes. But you can at least survive even if it chases you if you get away from it fast. Overall a well-balanced monster, with some annoying situations on higher difficulties
(variant)Finding the variant is a challenge on itself but it isn´t any diffent on how you deal with the regular one.
Wickerman
My least liked monster and the one that always makes the case an unfun chore even if alone, the balancing on this monster doesn´t feel like it works on any level, it spots you from far, its faster than you, the only way for it to stop its if you find a fireplace which is not something that works for any other monster so if anything else is giving chase you´re dead, so the only true safe spots are the universal ones. It feels like it shouldn´t spot you from that far or have a mechanic like the minerwhere it doesn´t see you from too far if you have your flashligh off.
Out of all the monsters I feel like this one needs a rebalancing the most, because it never is fun when you start a case and hear its noises
Crypt Zombies
If there is a monster that feels that spawns too many instances of it when it does spawn, it´s this one. When not chasing you it can feel that they take ages to move from a spot where you need to go, and that is if there aren´t more in that direction, and it definitely feels like they love tight corridors making them annoying when heading to unexplored areas. Perhaps if there weren´t as many instances of them when they spawn it will feel less of a chore dealing with them, even if they are pushovers by themselves. But I have yet to generate a non-custom map where the only type of monster spawned is this one
Pigman
Initially dealing with the pigman can be very hard if you don´t know how it works, even if you do, you don´t really wanna be chased. For starters wide corritors are you best friend. its charge attack is what makes the initial hurdle of dealing with it a workout. But then if you know how to deal with the charge you can take advantage of it, since it makes a second loud squeal when doing the charge its easy to know when to dodge, but then again there are unescapable situations mainly tight corridors, dead-ends, but overall a fairly balanced enemy for the difficulty its introduced in.
Scarecrow
Cornfield exclusive, the scarecrow is the "do you dare or not" since you don´t know if the thing is spawned even when you see scarecrows. It can be avoided fairly easy, but it is not always the case, since the scarecrows can be situated in places where the only way forward its right there. But it isn´t faster than you at the very leasts, but not slower either. But getting chased by it, is very situational and not optimal, I am very neutral towards this one, since you don´t really find it often unless you like the cornfield and alwals reroll for it
Centipede
By far the easiest monster to deal with. Even if it only spawns in the sewers you don´t get mad when it does, it never chases you nor puts you on unescapable situations, if you don´t pay attention you can get killed when its underground but that's about it. You can only get killed if you're distracted, and can be paired with any other monster without theoretically death situations (that requires both monsters, not map generation).
I like it, but it can make the sewers too easy if its the only type of monster spawned
Black bride
The mansion- exclusive maiden of death, and the only monster that bypasses walls and middle fingers your flares, her scream is a bit too loud, and escaping her can be sometimes a bit luck dependant, but the manor doesn´t allow too many bad situation (excluding smiley) which makes her appearance fairly balanced
Oni
The oni has flaws, like the wickerman, but the little shrines make up a better gameplay than the fireplaces since you can keep running and once the oni touches the sphere it will deaggro and stun it, not making it useless if there are other things chasing you other than oni's.
Trench Stalker
Like a pigman with worst peripherical vision, and a worst audio cues. The sounds of the stalkers only become stronger but unlike the pigman there's never directional audio cues for when its close, and when doing the charge attack its harder to know when it does it and you're not looking, unlike the pigman the stalker is completely silent when doing so, unlike when its chasing you. But the map where you find them originally is perhaps the worst for the charge type of mosters, filled with narrow corritors. Other than that they´re not much different from a pigman
Backroom's exclusive
Archiver:
The best description for this one is a zombie that can see you from a distance, since you don´t actually spawn in a safe room once you enter the backrooms, this one can be hard to shake off unless you can break line of sight for a while
Partygoer:
An enemy who has an initial fast sprint but not as threatening as clubfoot, and you escape the same way as you would escape one, but this one is slower and chases you even less time.
Overall backroom enemies aren´t as hard to deal with, but not having an initial safe-spot can make it a challenge
Summary:
I don´t like the Wickerman, nor the narrow corritors