A cosmic entity created by Howard Phillip Lovecraft. Yog Sothoth is an Outer God that is thought to be time and space themselves or at least be highly connected with them. It is often described as being a conglomeration of glowing spheres, although it has many avatars of different appearances. One such avatar is Umr At Tawil.
It is known to be the offspring of the Nameless Mists, created by Azathoth.
Yog Sothoth appears as an optional boss in the Extra Dungeon. He is fought at the end of class 3-A in order to obtain the White Butterfly. After being defeated, he starts appearing as a normal encounter.