This is an interesting fight. Master Pandemonium got steadily more powerful as he absorbed more pieces of "his" soul. Until he absorbed the final piece and collapsed into himself and Mephisto emerged.
"His" soul was really pieces of Mephisto that Franklin Richards shattered into 5 or 6 parts when he wtfpwned him.
Master Pandemonium with 5 (or 6 parts can't remember) of "his" soul should own Hulk hard.