Magus

Magus is a Sorcerer that instigates the bout of Player Killing and enslavement of weaker Adventurers by Hamelin, although he does not belong to the guild itself. He is only seen in the West Wind Brigade manga.

West Wind Brigade side-story
Magus first appears when Isami confronts two Hamelin guild members, who are trying to force Touya and Minori into joining. Under the guise of trying to help the two newer players, he successfully deflects Isami's suspicion and recruits the two children.