|Real world information|
Yog Soth-oth is a demonic being from another dimension who appeared in Big Trouble In Billy's Basement.
HistoryYog possessed Billy through The Bad Book in order to be released into the world. Billy then stole The Reaper's Scythe and opened a portal between dimensions.
His work is immediately recognized by Hoss Delgado, who reveals Yog is from another dimension and that "bad stuff is about to go down."
Billy then comes down and proceeds to fight the group, until Grim steals The Bad Book back to figure out how to get rid of Yog, by throwing the book into the portal.
However, Billy swallows the book, and is seemingly triumphant, until Mandy pushes Billy into the portal to get the book into it.
- Yog-Sothoth is based on the eponymous creatures of the Cthulhu Mythos, like the subsequent character Cthulu.