@FormerCrimsonKing: Wow, I never realized Blackheart was that powerful. He actually has many
similarities to Buu. I could see this being an almost never ending
battle. Both are matter transmutors, both have hax regeneration,
Blackheart has mindrape and Buu has telepathic immunity or extreme
resistance, Both are planet busters, Both are teleporters, both can rip
through space and time, etc. Idk, I see this as a very long battle with
the winner depending on plot.
@FormerCrimsonKing: Hmm well I don't know about omnipotent but I do know that all those marvel super sorcerers with their own dimensions are very haxed out. I guess you are right he would be head and shoulders above Buu there, but I think Buu could have a chance at escape. And if he could keep himself from being transported there in the first place he should do alright. But you opened my eyes to Blackheart's power. I guess it isn't too far fetched to say that he (Blackheart) could win 8/10 times.
I don't see how Buu is even capable of denting Mephisto's offspring. Immortality, essentially godlike in his Darkforce Dimension, ability to go intangible, soul manipulation, reality warping, capable of mind control on a planetary scale, planet-busting via telepathy.