This would have tied to the character's comics history, as Billy and Tommy's souls were originally part of Mephisto himself before Wanda unknowingly used them to create her sons with her powers.

They are fragments of a villain called Mephisto’s soul, which he comes to claim by reabsorbing them into his body. In the comics, Agatha Harkness wipes Wanda’s mind to spare her the pain of ...

With Robert Downey Jr. coming back to the MCU as Doom, we could see Mephisto factor into Doom’s arc. When Wanda and Vision ...

He mocks Vision, drawing Wanda’s anger. And some people speculated this Quicksilver might not be who we think he is. He might be Mephisto, one of the Marvel villains shortlisted for this ...