Battle of titans here I think, and I was so sure I could find some hits, but 'death vs Mxyzptlk site:comicvine.gamespot.com' search on google didn't even find anything.
So, I thought I should get a definitive battle and answer. Also,
The Eternal Crush of the Mad Titan Thanos,
The Mistress Death herself:
The one and only superman villain who is so powerful he just wants to mock him all the time for giggles:
, as too op, and fictionally righting outside of comic book, etc.