This horror mod adds SlenderMan, he will spawn in your world at night, SlenderMan has 100 hp and can teleport and if he hits you, you will get blinded for 5 seconds

If you manage to kill him, you have a chance of obtaining a Soul, if you get 4 of these and put them in crafting table you will get Agony, it's being used to craft different things such as:

Cursed Microchip that allows you to craft Camera wich prevents you from getting blinded while fighting SlenderMan

SlenderMan's Sword, it has 900 durability and 10 damage

SlenderMan Totem wich will spawn SlenderMan Boss, true slenderman's form, he's much more aggressive and dangerous, to craft this totem you will need to collect 8 pages, they spawn in different structures in all types of forest biomes, after getting one you can put it on wall or use them in crafting.

During the night you might encounter Proxy, this mob is controlled by SlenderMan and will attack you, also might drop Soul

Proxy texture by HoldOn

SlenderMan: Reborn