This game is hardcore and taking down weirdos take lot of hits, even more if you don't have fight abilities so, for all of them, the best option is always to run and hide instead of fight back.
There is a situation anyway that make the fight "easier".
Being in a safe room:
Weirdos can not close door, just open it. In some spaces such maze corridors you can create a "safe zone" by leaving the door open, and eventually you can hit trough it.
Not gonna discuss too much about HP because with this guide you mostly focus to understand the weirdo and survive it so just remember each floor increase a 2.5% of the enemies stats such HP, DMG, etc... and you weapon deals full damage only when fully charged.

For the rest, always keep in mind where portals and showers are. Weirdos can chase you trough stairs so it is better to hide somewhere else. If you are in danger go to a safe room, portal or shower and that would be good enough to make you survive one more minute.

The first enemy you could possibly encounter. On floor 1 is the only type of enemy it spawn (on normal mode or easier at least). Bewere there is a tiny chance a golden minion will spawn and it has around 5000 more hp than the regular one.
How to counter:
50% of possibility that the Minion cannot open closed doors so try loop it in a room and leave closing the door behind. If the Minion can open doors than use teleport ability or lock ability to lock him inside a room.
If you kill it, 2 Minions will spawn on the same floor so if you kill too many Minions soon you will be invaded by a horde.

Simply a summon circle. You can use Weirdo's essence to summon a specific weirdo on the spot or use your blood to summon a random wierdo.
How to counter:
Just don't touch it.

The sweeping angel of the game. If you don't look at it, it could eventually try to hyperspeed to you and break your neck, intantly killing you. There is a 50% chance the Scarer is fake. If the mannequin was real it will ragdoll on death dropping stuff but if the mannequin was a fake one it will fall on death like a statue.
How to counter:
Scarer tend to be close to walls. Always look on corners when you enter a room. If there are multiple mannequin try to keep the others in your sight while killing the first one. If you have no weapons you can push it away, maybe putting it in a room and close the mannequin there since it can not open doors.
It is reported that fake mannquins can eventually roteate in position when you don't look but real ones change positions and try to get closer.
Sometimes you can see Scarer moving very slowly.

Simply a weirdo that disguise as a vening machine or a safe. If you touch the mimic, it will bite you back. The vending machine deal around 80 dmg and the safe around 40 dmg (also the safe will eat your key if you tried to use it)
How to counter:
If you stand next to the mimic, you would sometimes hear its breath. Mimics can be killed but this take a lot of hits and will attract more enemies on your position (for silver safe mimic could take even longer to be killed and a gold safe mimic has around 5000hp not including the moltiplicator for the floor).
If you have a safe spot, pharaps next to a portal or inside a safe room (see above what safe room means) you can kill the mimic whitout consequences and teleport the hell out of there.
Bewere it's bite is AOE so it will damage all players around it.

A weirdo that will imitate you or your teammates. It is quite relistic since also imitate the equipment and act like a real player, running around like he is escaping from something or starring at you when you approach. the Mimic is mostly harmless but if you get too close it could fight you untill it loose you.
How to counter:
Mimics can't duck, so, if you are not using discord calls, since there is no vocal chat, you can show you are not a weirdo by just ducking. Also, they don't drop items, can't spin on spot, don't interact with the loot... in a nutshel, they lack the complex behaviour of players.
Just avoid them and don't get too close.

This wierdo is the only one you can't kill in any way possible since it is intangible. Jareer will teleport you one (some say even 2) floors below if it has the chance.
How to counter:
It is attracted by the sound of looting. You will hear noises like footprints on wet mud or like splashes on shallow water. eventually red handprints will appear around you. Get far from that zone because it is about to teleport you. After a while you can go back there doing your businnes.

It is a oversized wooden toy with metal dishes. When it clap the dishes 4 portals of different sizes will appear close to it. If you stand too much on these portals you will be teleported in a random room on the same floor and the door will be locked, so if you have no key with you and no weapons to kick the door open (remember that hit doors attract wierdos on your position) than is game over.
How to counter:
Just avoid it, it will try to run away from you. If you want to kill it try do it in a open room where it can not run away and you can avoid portals easly. It has a chance to drop a eyeball that will heal you and teleport around the floor, great to avoid dangerous situations

It is little and has a flashlight helmet on it's head. Eventually in the dark you can mistake it for a flashlight dropped on the ground.
How to counter:
Just dance around it, even crouched, or jump over it while you beat it to death. Its attacks are very slow and not so powerfull.

Consider it like an upgraded minion. Can open doors (not locked doors) and its special ability cage you for some seconds blocking your movements, like when you step on a beartrap.
How to counter:
You can bait its slowest attack and hit him back during animations. On higher levels it is faster and stronger so team up with friends to kill it. Otherwise just run away

A gnome size weirdo that will try to steal your sh*t starting by the flashlight. After the Picker will steal something it will run away but will come back to steal some more
How to counter
You can buy an ability that will prevent the Picker to steal from you, so instead it will just punch you but doing so wont deal too much damage. If you fight back, at low health, the picker will try to run away. You can bait the picker in a room so it will be stuck and wont flee away while you beati it to death. If you have not the ability, be sure to fight the Picker with lot of weapons otherwise just run away.

There are 3 type of this weirdo based on the color of the dress.
The black one will mostly scare you.
The red one will mostly attack you.
The white one seems balanced on attack and scare.
When not aggro she will roam around very slowly and eventually you can hear her crying.
How to counter
When she sees a player she will become invisible but you cannot hit her in this phase. She will eventually appear to scare you (by making a jumpscare increasing your fear level or by screaiming at you making drop your equiped item) or to attack you from behind. During this moment she appears you can hit her back. She take a while to be killed since her attacks are not frequent but has low hp.
Eventually you can use the ability to mark her so you can follow her movements while invisible.
She will sprint to your location when invisible to cover the distance, so if you want to flee try interrupt the line of sight like when you flee from any other weirdo.

It is aticipated by a running red light in the corridor. If you are in its way it will crush you but with some resistences or full hp you can tank a hit.
How to counter
Showers on corridor's corners prevent to be in its line. If you plan to run in the corridors to move around the floor than always run on the opposite side of where it goes. It stop for a while on the corners before charing again. On higher levels it stops for less time so it roams more frequently. You can eventually kill it when it is idle on corners but has a hell of HP so is gonna take a while and don't pretend it will stay on spot to be killed.

It appears not less than a man with a siren instead the head. When this weirdo attack you it will eventually scream its siren attracting more enemies to that location
How to counter
It is tougher than zombies and prolonged fight with it can attract more dangerous wierdos. Try to dispatch it as fast as possible. Can be attacked while its animation to scream the siren but this attack also rise your level of fear.

That wierdo looks like a jacked noob saibot from MK holding a crowbar.
It is very fast and can hit multiple time in one attack.
How to counter
Kinda harder to fight than the Speaker and the Wanderer but has a higher loot since on death it would eventually drop a crowbar, keys or even a golden ticket. On death, all doors will be locked on the same floor so if you have no keys or weapons you are dead. Eventually kill the Keyper on the room below the staircases or next to a "above portal" so you have not to waste resources to get away from the floor. It instantly open locked doors so do not waste time closing doors behind you if you flee but just try to lose line of sight or hide in a shower.
It is tough and his attacks are multiple and hard to read, even if slow.

It is a floating dark ghost with red eyes. Eventually it sees you before you see him if you go around with the flashlight on.
How to counter
Suggested to run as far as possible since fight the Darkner will increase your fear level incredibly fast and since there are no item on game that cure "fear" beside these cheap candy or the calm ability, a prolonged fight lead you to a quick death.
Is the third enemy with the most health and takes a lot of damage to kill it and as mentioned it doesn't do much damage to the player but increase the level of fear for each hit, also looking at him will increase the fear level.
Try to avoid it as much as you can.

It looks like a guy in an armored vest, surrounded by green gas.
How to counter
Every attack can hit multiple time and also will give toxic damage so deal with it must be a hit and run but damage is almost inevitable. Also seems to be able to open locked doors so teleport it or lock it behind a door would just buy you some time.
Its gas cloud from the orbs can also hit you when inside a shower so try to avoid this situation.

It is a ball with theets that roam around. It roam around the floor producing the sound of a squishing ball. If it sees you than will spawn 2 more balls that will chase you, eventually biting you to death.
How to counter
It is as fast as a sprinting player so even if its kisses wont deal too much damage we can say it would eventually tickle you to death. Killing it wont give much good since it will drop a bear trap and little bit of resources on the ground. If it spot you on the corridor be lucky enough to close yourself in a room untill it lose interest or to lock yourself in a shower. Can be baited in a room, jumped over and since it can not open doors, at cost of some hp lost, you can safely lock it away.

As the name suggest it is quite deadly. It is a zombie like monster with no face and no eyes roaming around with two machetes. It is anticipated by a loud heavy breathing and your flashlight will turn red. It has an insane ammount of HP making impossible for a normal human being to confront it in a fight. Since it uses the ears to locate you and not the eyes you can't even use a potion of invisibility against it.
How to counter
Stay still. When it is close to you just moving the mouse wont trigger it. Any other action such opening doors, drink, eat, attivate stuff or use abilities will trigger it and if it is too close when you do any action than the Reaper will start to attack you. the Reaper will eventually come close to your position and after a while it will leave returning to its roaming fase. If you are in chase locking door will just slow it, so losing line of sight is quite hard and showers are the best option.

a human-lizard like weirdo that is considered the deadliest of all (beside the boss). If it see you it will try to grab you and you will have to escape its grasp by spamming E.
How to counter
If you see the Lamper you can consider to leave the floor as fast as possible. Locking doors will just slow it so lose line of sight is quite hard. Showers are the best option.
It is around 6 times tougher than a regular minion but eventually with some pratice and the right ability to not let it grab you, you can fight it back if you learn its attacks pattern. A lot of "if" for a monster, so just cut it short: run away.

You will find it one level above the last floor (45th floor on normal mode)
After a brief introduction it will stand still on the room giving you the opportunity to kill yourself. If you attack it the boss fight will start.
How to counter
It teleports around the room whenever you hit it. If you give it tooo much time it will snap the fingers and attack. The attacks are:

• Markimoo will jump on air and on landing he will produce red shock waves that mostly insta kill any player. You can jump over the waves to avoid damage. can spawn up to 3 consecutive waves.
  
• Markimoo will spawn a random wierdo than jump and leave the boss room for a minute. It seems that the wierdo dies over time but seems to not be the case for all. You can prevent it by drinking potion of invisibility and kill it before Markimoo comes back. Yes, can spawn the reaper. This is the most luck generator situation you can encounter. Consider to bring the "pacify" ability for the bossfight.
  
• Markimoo will make your active weapon fall. You can prevent it by having no item on hand when it does so, but most likely you just have to pick your item up.
  
• Markimoo will spawn 4 bear traps around you. Seems the bear traps will last for all the duration of the boss fight.
  
• Markimoo will spawn a turret in its position that will fire lasers. Some of those lasers will be stationary but other will eventually spin. You can avoid it by jumping or ducking. Carefull that being farther from lasers means these will spin faster. If you are below the turret when it will spawn, it will most likely crush you on spot.
  
• Markimoo will spawn some giant sawblades and than launch them and high speed around him. The sawblades are aligned with the shooting line so you have a second to get away from the line.

As far as i understood the fight doesn't depend on damage but on amount of hits you deal, but I wont say for sure.