1. Eternity – The personification of all that exists across space-time and the entire multiverse. Characters like Sentry can’t even interact with Eternity because it's an abstract cosmic entity. No Eternity = no Marvel Universe.

2. Celestials – Among the strongest beings in the Marvel Universe, they serve as cosmic architects.

The Celestials created the Beyonders, the most powerful races in Marvel. Beyonders nearly wiped out entire Marvel multiverse in New Avengers.

In Fantastic Four Annual #26, Kubik says to Kosmos (a female version of the Beyonder) — "The Celestials could have easily crushed you."

3. Scarlet witch — One of the most powerful reality warpers in the Marvel U

niverse.

I’ll leave out the rest since their power levels are dependent on narrative. Eternity, however, will always stand at the top. Though there's also The Living Tribunal.