Killer

The killer is a non-symetrical monster, meaning that it can spawn at the start, he is a black man with a creepy smile, black suit and uses christmas lights as eyes. It's ability is to be the 2nd fastest monster in-the game (Dummy being the fastest monster), running about 1.5 times  the player's sprinting speed, while also making the player faster but using more stamina and being unable to regen it, but can be regained by eating cake spawning around map.

Hard mode
In hard mode, Killer deals 60% damage and takes a very short time to spawn on each room, being very bad if you have a bad internet.

Tips

 * Even with its ability to not let the player regenerate stamina, you can regen it every room you pass, and by eating the cakes it spawns.
 * When in long rooms, try repeatably pressing shift when you run out of stamina and dont have cake (watch out for sticky keys).

Trivia:
Killer was originally made for a project that was cancelled sometime in late 2017.

Despite his name he's the only monster that doesn't directly kill the player.

It is one of the only enemies not to have an introductory room, spawning randomly through your gameplay.