Blackheart is the son of Mephisto and second-in-command at Mephisto's Realm.
Blackheart is a sadistic demon who gives a victim a decision, in which both answers will have terrible consequences. This is shown as Blackhert captured Jean Grey and Nightcrawer and made a team of heroes decide which one of them would live and which one of them would die.
Sunboy's take on Blackheart was the earliest version to exist. It takes after Marvel Super Heroes. It contains gameplay accurate to said game, even with the infinity gem system present. As an added bonus, it also has a new Hyper involving Shuma-Gorath, as well as a Hyper that wouldn't appear until Marvel Super Heroes vs. Street Fighter.
This version is a MvC styled version with 3 Hypers. This version uses most of Blackheart's powers over the underworld including electricity, ice, fire, and summoning minions to attack and immobilize his enemies. He is however sluggish in movement and has a slight delay in attacks with a short start up and cool down time. A.I. Plays sluggishly and slow and is quite block heavy. Rarely using any Hypers during the match however it can be surprisingly challenging at times. Overall this is a good version as it does not have any bugs or game influencing glitches which affects game play and can sometimes be a challenging opponent.