Mephisto planned to have Itsy Bitsy created and wreck havoc in Spider-man and Deadpool’s name. His grand plan was to drive Spider-man to kill Itsy Bitsy and tarnish his soul. Good thing Deadpool had Spidey’s back and killed Itsy Bitsy himself and spared Spider-man from doing the deed.
From – Spider-Man – Deadpool #18
It’s also his fault for causing all of this. All could’ve been avoided if he didn’t assassinated him in the first place, then brought him back to life.