Injustice 2: 10 Incredibly Powerful DC Characters NetherRealm Left Out
6. Jason Blood/Etrigan
With Etrigan, you get a two-for-one multibuy sort of deal, since the ancient demon is permanently bonded to Jason Blood by Merlin. A venerated occult expert, Blood might be a vulnerable human, but he is ageless and immortal (provided he isn't harmed), and he has shown considerable magical powers (like opening a portal to Hell, defensive magic and magical blasts).
As Etrigan - the demon form he can summon by saying a poem - his power levels jump almost infinitely. He's a hugely powerful mage and is strong enough to stand up to the likes of Superman, Lobo and Wonder Woman, with an admirable healing factor balled in for good measure.
Just imagine playing as him in Injustice: starting as expert hand-to-hand combatant Blood, and only able to transform periodically (or after charging up) to Etrigan to change things up. It's a hell of an idea.