2. The Beyonder

He was first presented as the most powerful being in the Marvel Universe, the be-all and end-all of the “Beyond Realm” who took human form to understand human race better. The original Secret Wars described him with powers million times greater than the multiverse combined. With a wave of his hands he sent a gathering of demons back to hell.

The Beyonder was originally created as a great force but he was re-tooled. This diminished his power, but his original form shouldn’t overlooked: he fought off Galactus, he created a universe out of his own being and destroyed a galaxy on a lark.

If he is going to come back in his initial form, The Beyonder might cause a lot of destruction.