Blackheart and Mephisto are both pretty powerful demons in the Marvel Universe. While Mephisto may seem to be a lot stronger since he’s higher up along the food chain, he hasn’t gotten to fight as much as Blackheart. Blackheart was a playable character in the MVC2 fighting game and he has a lot of attacks. Physically, Blackheart is very powerful and he’s a much better fighter than Mephisto. Mephisto has energy attacks, but so does Blackheart. Youth will usually trump the hierarchy. Blackheart wins.