Nemesis, provided it isn't the weakened version that we saw on the story.
Nemesis, was, for a lack of better term, a portrayal of god in its entirety. The story suggests Marvel multiverse and Malibu Multiverse were born out of the left over energy from Nemesis committing a cosmic suicide.
Sadly we don't see Nemesis fight anyone in the story. I mean when you are pretty much called a God who would you fight. She does erase universe with a blink of an eye and erases infinite copies of heroes from both marvel multiverse and malibu multiverse with just a thought leaving only the original ones as a template.
Nemesis is a character ill suited to battle forum because we have no clue as to the upper limit of the character. The only thing we have seen is a weakened version that was going through internal struggle from each gems having their own agenda and even then her showing of power drawfs anything we have seen from Marvel, perhaps barring HOM Wanda.