Ex Nihilo may think he is the all-powerful being, but Kirby isn't just any puffball - he is the strongest being in the parallel universes and has killed multiple gods without even breaking a sweat. Kirby also has the power to copy the abilities of his foes, so even if Ex Nihilo can create anything out of nothing, Kirby could easily copy those abilities and use them against him. Plus, Kirby's power and guard are far higher than Ex Nihilo's, and with the added bonus of speed, there's no way Ex Nihilo stands a chance. Kirby simply cannot be stopped.