Horrific Heights is a mod which adds some very scary things to minecraft

New mobs:
Stalker: Tall man
Runner: Ridable beast
Watchling: Unstoppable monster
Watcher: Eyes
Eye: Small eyes
Eye Of Cthulhu: Huge boss eye (may crash your game)
and more to come...

New Dimension: The Middle
Adds the demented forest

New armor:
Avidhal Op armor used to kill the stronger beasts