I just checked and Sapna's mutation is not directly summoning and controlling demons.
She was like Cypher + Prodigy on steroids:
So, it was just magic.According to Doctor Strange, Sapna has the ability to absorb, translate and fully understand the languages of anything and anyone around her. When her powers manifested, Sapna was in Limbo, which prompted her to absorb all the magical knowledge from the realm.
Apparently Chimera is not a mutant.
Great issue <3 Magneto was sick af.