I will call the Unknown Specimens "Entities" just for the sake of simplicity, and also because it doesn't make sense calling them numbers if they don't appear in any specific order in-game.
Otto is just a joke character made because FNaF fans where bothering too much, he moves slow, attacks lightly and even slower, and is an non issue to worry about like...ever.

Without a doubt one of the easiest enemies to counter, they basically appears in groups randomly scattered around rooms blocking your path, a couple of axe/sword swings can do the job but watchout that sometimes they wake up and attack you, tho they are not much of an treath even when paired with another stronger enemy.
Even tho the wiki says they chase for a lot of rooms and that you should keep one around to take space that another stronger Specimen could, in my experience they don't last more than 10 or 15 rooms.

He is one of the four weeping angels this game has, and he is the only true weeping angel since he stays completely still when being stared instead of slowly moving towards us and just straight up teleporting right away when we look away.
The ONLY reason he is above the Husks is that he is a solid entity that means even if he is docile he can still block your path and the fear that he might get us softlocked in the infamous U room with a locked door is enough to give me nightmares, since the game doesn't allow us to quit when he is chasing us like if he was an hostile Specimen and leaves us to Specimen 9 to come take us from our suffering.
At least he takes space that a real threat could so that's a point to him, he also flicks around the room before appearing on the entry door.

Other than the fact they stop you completely on your tracks for one second when they appear, block your back when you have to stare the weeping angels and almost give you a heart attack pretending to be the baby head in a box at quick glance they don't pose much of an threat.

You will never meet this guy if you keep moving your character, tho he can still kill you with the game PAUSED my brother! That's an annoying aspect of him that makes me hate him rather than liking because he is interesting in both concept and design.
There was a time where I paused the game and left for just a couple of minutes, then I came back and looked at my paused screen and the game just played the CAT-DOS custscene right on my face, mind you it was in a Endless Mode run...so yeah one of the most interesting creatures in this game reduced to an annoying brat that keep pushing you to play even when he shouldn't.

He alongside the Cardboard Cutouts are the only enemies you will face that can chase you from the very beginning of your run, even before his introduction room appear.
He is easy to handle even when paired with other Specimens since you can hit him with the axe/sword to give you some room to breath, tho his slime puddles can be a real nuisance when there are speedsters enemies alongside him like the centipede or the bodybag, but when walking on the puddles is best to stop running and letting you recharge your stamina to run when you get out.
There's the fact that he alongside Bab and the Old Man can chase you alongside the Mermaid, and in his case he can bug out and float towards you with his arm down and completely motionless wich I find really funny when this happens.
He doesn't make slime puddles in the Mermaid's flooded rooms wich is a nice thing but he can float over pits in normal rooms, wich is nice too since you can hit him while he is hovering above a hole to send him to the shadow realm.

He appears randomly around rooms outside the walls and come straight towards you, it seems like when he appears far away his speed increases too, you can hit him with the axe/sword a couple of times to get rid of his chase but it will take a lot of uncessary time since he teleports to another place after being hit.

He is not a problem when alone since he is old and can't run for much long, tho his hits still pack a punch and he parry our attacks so it's best to just run and avoid him.
My only worries with him is the infamous U room with a locked door since he can't even run in the flooded rooms of the Mermaid.

Even tho this...entity...is the overarching villain of the Karamari Hospital DLC it still doesn't pose much of a threat when chasing you alone, since well...you can just kill it right away when it spawns.
Tho if you can't kill it beacuse you're running from another enemy worry not because the only issue this Monster gives you is the black fog on your screen.
It can float over pits and also changes the layout of some rooms to match it's labyrinth room in the Hospital, and also makes the walls be iron bars that help us see ghost type Specimens through.

He is an ambush+speedster enemy, taking out the fact that he can block your path he is not usually a big issue, he appears from the entry door or randomly spawns somewhere inside the room, he is really fast and deals good damage but stops to attack and that's his big weakness, besides that he can be hit a couple of times when he bents down to attack to kill him.

A LITERAL DEMON, tho he is quite easy to deal with since with good knowledge of the rooms his gimmick to hide the doors are not an issue, he also has this glowing fire crown above his head that let us see where he is inside walls since he can faze through them and also float above pits.
The ultimate aspect that makes him easy is that he can get hit by both the axe and the sword to make him disappear for some time.

It can only chase you once in your whole run...and the Mermaid managed to steal it spotlight right when I was entering the space-void room with the cute pink cat, and she alongside Old Man kept bothering me till the next elevator...
It is an easy Specimen to handle since during it's chase(not the rooms before it) no one can join in and the challenge consists of maze-like rooms with distractions on the walls, and of course the red wall with the souls of the damned in it closing in on the exit door, it kills instantly upon touch but is so slow that it is not a big issue.
The only reason it is in B tier is the insta-kill possibility and that you will meet it some time, unlike Taker that you will usually never see.

Welcome!

He is an weeping angel type enemy where we have to stare at him to make him stop in his tracks otherwise he teleports to us and almost immediately attacks us, removing a good chunk of our health.
He can also move by himself if we stare at him for much long, and also can be hit to make him useless for the current room and also reduce the duration of his chase.

The first real threat of this list without a doubt, she moves fast, hits hard as a truck an can obstruct your vision with static and hallucinations that depending on the room they can really mess you up.
Unlike the Old Man she just tanks your hits like it is nothing and also a nightmare to the infamous U room with a locked door.
The only thing that keeps her from moving up in this list is that she is a ground enemy, having to walk the same path as us to reach us.

Look at this adorable little fella :3, it is an ambush+speedster enemy much like Charles but instead it has a chance to spawn from the entry door or fake out and only spawns when you walk up next to a ceiling hole, where it will drop right on top of you but fear not, it can't deal damage while in the dropping animation.
You can hit it to push it away from you and it has quite a difficulty to make sharp turns, it also back off when it hits you.

The first real threat of the Story Mode, she can faze through walls, hover over pits and is really fast.
She is an speedster and can easily catch up to you in spiral-like rooms and her attacks deal a LOT of damage for an enemy that has a short cooldown and keeps glued to you when reaches you.
The best way to avoid her in spiral rooms is to let her reach closer to you then sprinting away to the next turn of the corridor.

He is invisible from behind, other than that he behaves just like the Centipede in that they speed up when moving in a straight line, but this one has a real problem making sharp turns, He is also immune to the axe/sword unlike in the Karamari Hospital DLC where we can kill him with the sword.
At least he teleports back to the entry door after he gets to hit you.

Praised be Bayagotoh! One of the best monster designs I've ever seen!
Both him and Toriel are goat monsters that made their debut close to one another and call the main character "child"...hm...interesting.
Nonetheless he can faze through walls and hover over pits just like Ringu, with the difference that he is slow but can teleport right in your face if you go far away and there's a wall between you and him.

THE.MOST.ANNOYING.SPECIMEN.EVER.

Every time she appears there will be a normal room before the flooded rooms starts, and oh boy when it starts...
She swims under the water and of course the water slows you down, but you have the crates to climb up and rest a little while she goes away from you, still it doesn't change the fact that is a complete chore to escape her evey time she appears and she last forever too.
If you get her first, quit and reset your run because she will appear every chance she gets and on top that she has priority over all other Specimens, that means when she appears she will rule over the place and only Specimen 2, 5 and 12 can join in.
There's only one saving grace from her is that when she appears she blocks any other enemies from spawning outside the mentioned list, wich is good that you can't get death comboed but still it takes a lot of time to get rid of her and she can rechase you just like any other Specimen.
In Story Mode she is an epic encounter but here in Endless Mode she overstays her welcome, and mind you there's a room where she spawns right in front of your face and is an almost guaranted hit specially if Lub-Glub is together, and if you're being chased by Bab or the Old Man as well you will almost die in that room.

Yes she has a 3D model in Endless Mode, but most of us doesn't even get to see that because of how rare is to encounter her in a run, it's easier to die before she even appears.
She basically can end your run if paired with one of the speedsters Specimens just because she appears from the exit door and forces you to back away till she disappears on her own, and on top of that your screen have a dense fog while she is active on the chase.
But if you get lucky to appear inside a room with multiple exits you can pick the one that she is not guarding since she only appears in one of them.

Cough cough, eh...well she is Deer Lord's pretty cousin, but it is as if Lub-Glub had a child with Ringu because she is a ghost slow as hell but spawn those shadow animals to physically block your path, that means even if she can faze through walls and fly over pits you can outrun her till you get bodyblocked by a shadow with the most broken collision hue ever, wich in this case you are forced to waste stamina to cut it down instead of letting it recharge like Specimen 2 puddles.

Don't you love getting killed by obscure forgotten characters?

Props to Akuma for animating his pixelated face and drawing the realistic one! <3

I have a great respect for him since he is the only enemy who gives you a second chance if you die to him but you must earn this second chance.
Basically he acts similar to Baby Head and Bekka appearing from the exit door or outside the room and bee lining towards you.
He flicks your screen with black and red and makes a static sound whenever he is too near, and also you can hear a raspy breathing(smoker breathing) sound coming from him to facilitate localizing him.
He disappears after chasing you for some time and appears far away so you can advance in the room.
His chase also last quite a while too, wich can help with being comboed by harder enemies.

Now as for his mercyful approach is that whenever he kills you he says that DEATH IS NOT ESCAPE then speaks directly to you player saying that your body is closed and that it is a shame, then he gives you a prompt writen "CLOSED" on it.
You should delete it and write "OPEN" and click enter, after a quick jumpscare you are sent to a sequence of rooms made of flesh and now you have exactly 1 point of health and your objective is to run from him till you get to the normal rooms again.
Inside the flesh rooms you can see him in the dark, and he also doesn't faze through walls like he usually do in the normal rooms, after running for some rooms that doesn't count to your room counter you are sent to the normal game and your health start regenerating like usual.

If you are being comboed to death by hard enemies and he is present you should throw yourself into him so you can save your run from ending prematurely.

The voices...are getting louder...

This is one of the most middle finger creatures added to the game, since the game can make the enemy theme music don't play on purpose this man can just jumpscare you out of nowhere during a rechase.
He behaves like Ben, but instead he slowly flicks closer and closer to you even when looking at him.

Do you have games on your phone?

I fear no man, but that thing...it's scares me...

But seriously, this Entity will spawn at the most random times just to mess you up, like one time Lisa was chasing me and this dude kept blocking my door and I wondering why I couldn't open it.
He was known as the Run Ender by the community for the ammount of things he alone could do, but after the nerfs he got more tame and winnable.
He will initially appear(and teleport) to the exit door closer to you and you must hit him a couple of times with your weapon to make him vanish, after a couple of times doing this he will disappear for good and the rooms will look like they where corroded by acid and your health will start draining till you die or escape him, and your healing is disabled since he doesn't give you time to rest.

Even after the nerfs he still do lots of things that are worth noting:
-He drains your health in a set pace, that means your life is in a timer that can only be stopped escaping him;
-Randomly makes you throw up and lose a good chunk of your health, and is always on the most incovenient moments possible, thankfully he can't do that anymore when paired with another enemy;
-Make you see hallucinations that can distract you from the exit door;
-He still is the Run Ender if you get paired with one enemy and gets hit by it or throw up then gets paired with another enemy, since every drop of blood you waste matters when Spooper is around;
-The game has this "Troll Room Generator" where it gives you the same exact room a couple of times in a row, so if you get those big abyss maze rooms you are doomed.

Gotta love when he appears two times in a row since like the Mermaid he likes to appear whenever possible.

She definitely is a breath of fresh air after all weeping angels encountered in this game, she works the opposite way by having you to look away from her to avoid her attacks, tho she can still drain your health by touching her while avoiding eye contact.
She alone is not an problem since you can just look at the ground, but when paired with ANY other enemy she becomes a real nuisance since she likes to appear in the most inconvenient places to be, and there's also her fog that obscures our vision by a lot and when we are in the abyss maze rooms oh boy...
She doesn't mind being looked from very far away and we can also hit her with our weapon to push her a little away.

The reason why you wake up.

The last weeping angel of this list, her introduction is legendary in the original game since she doesn't have an introduction room, so you're just walking and then the rooms become red and the tension rises.
Although she is easy to deal when alone some rooms after her true chase begins the rooms counter will freeze till she goes away so you stay stuck there with her risking the chance another Specimen appears and bring the run to an end, since she can easily chip your health off you're not paying attention enought to her.
Leaving a problem this big unchecked is a fatal mistake that has to be done sometimes since you have to turn around to kill a certain Spooper guy or look where you are going in the abyss maze rooms, tho she will approach you and get invisible even while staring at her, so you have to memorize where she is even behind walls.
She is not much different from the other weeping angels mind the fact she can make your life hell by stunlocking your room counter and Monster-Stacking you to death.

And she also likes to appear two times in a row.

Oh boy...this dudette is the reason the Endless Mode is not so endless, she functions like Bab and Old Man except by the fact you HAVE to be near her, because if you step a little too far for her tastes she turns into a worm that barrels towards you at mach 5 and she stays like that even if you advance to the next room, she only turns back after hitting you.
So if she is paired with ANY enemy that is fast and immune to the axe/sword(cough Ringu and Body Bag cough) you can just sit down and cry because there's nothing that can be done to save you, unless White Face is present.

THE ABSOLUTE RUN ENDER

If you get her first just reset your run really.

The wiki says she moves slower when being stared but it doesn't seem like it at all, and also why would someone be staring at her?
Remember when Spooper was the end of the world? Yeah after the nerfs she got in his place, there's just so much going on for her:

-She is fast moving;
-She can faze through walls and hover over pits and holes;
-She hits hard as a train and has a short cooldown in her attacks;
-She keeps glued to you whenever she catches up to you, that means being comboed to death;
-She has this idiotic static barrier that a normal person in their right mind would never think in adding it to the game;
-And also she is of course a ghost so no hitting her to push her away from us.

She alone can give you a hell of a time in any place and any time you meet her, much more than any Parasite + Speedster can give.

She alone was responsible for ending my 2100+ rooms run by just spawning alongside the dreaded abyss maze rooms, and with the Troll Room Generation to help it was *mwah!* top notch.
Ugh...as much as I love this game I think she shouldn't have this many advantages, look at Spooper for example, they just reduced his health drain and made us stop from throwing up whenever someone is chasing alongside him.
I think if she just reseted to the entry door whenever she hits us would be a huge improvement already, and maybe increase her attack's cooldown too for the rooms that have the exit door right on the other side of a wall by the entry door.

Note I don't hate her and nothing like that, I'm just agitated that an Specimen that I didn't think much was the most powerful of them all, she could even beat Taker boss form and Spooky if she wanted.