Mastema

Devil Mastema (マステマ, masutema) is a fictional character in the manga series of Shaman King.

About
Devil Mastema is a demonic spirit that Lyserg Diethel fought during his training in hell with Pascal Avaf 's guidance. Lyserg's strongest oversoul - O.S. Mastema Dokeem, is named after it.

Anime/Manga Difference
Devil Mastema is a manga only character and never appears in the anime.