Gus Grim is a old friend of Dani Moonstar's. He used to work in Cheyenne communities. He is a cognitive therapist. Dani brought invited him to the X-Men's base, Utopia, after the events that transpired in The Fall of the New Mutants and The Rise of the New Mutants. She wanted him to help with the more damaged members of the New Mutants.
Unfortunately, when Mr. Grim made his visit to the island, some demon's from limbo, ended up jumping into his body and used him as a ride to Utopia. Once Mr. Grim went to speak with Magik the demons jumped out of his body and tried to free Magik. Fortunately for the X-Men, Dr. Strange had taught Danger, the X-Men's warden, a magical spell to vanquish the demons.