well, as that is the god of the Marvel Multiverse, they would likely have a similar power level to that of the Axolotl itself, so it is more likely to be a draw between Bill Cipher and the One Above All. As the One Above All can only affect the Marvel Multiverse, he likely couldn't just delete Bill, but the same thing applies to Bill himself, so I think it'd be a draw, assuming they were both fighting in the Marvel Multiverse. Switch to Gravity Falls, and it would be a totally different story.