Probably a lot of things. Chariot Requiem was quite literally a walking apocalypse, until they worked out it's weakness and beat it in five seconds flat. I imagine GER has something similar going on.

Discounting that: Nope. GER is one of those ill defined reality warpers that was utterly unbeatable, and then the story ended. That's as unbeatable as you can get without going into Suggsverse territory.

Anyway, here are all three things i can think of. It's not an impressive list.

• Tusk Act 4 - Infinite spin is crazy. It wouldn't be the strangest thing Tusk can do. Maybe it's just impossible to reduce Infinity to zero. Why the hell not.

• Some even higher reality warper - Heaven DIO did it somehow, so anyone on that level.

• Saitama - Well, you asked for the strongest who could beat him. See the whole "can't reduce infinity to zero" from Tusk4.