If that one mortal kombat line is to be believed and omniman really can operate at absoloute zero you can just forget about energy weapons because he can survive in an environment in which molecules are not moving at all. No motion whatsover.

The anihilarg from BEN 10 Omniverse,I think that’s what it’s called. The device is able to destroy a universe,while Viltrumites struggle to survive on the surface of the sun.Since the sun isn’t destroying the universe,the anihilarg could kill them all.

The omnitrix