Ascension can be considered a time when the rules of "god-modding" are relaxed, allowing a player to show their character as more powerful than they usually are.. however for sake of fairness even Ascended beings must have a weakness (especially if they are antagonists).
Normally this is dealt with in stories by having ascensions become unstable or prolonged, giving the other characters chances to strike down the opponent before they gain true omnipotence.
If the other characters fail to stop an ascension it is possible for an alternate-form to be born, usually embodying aspects of both the original character and whatever force/being they are merged with.
Ascension In The Villains RPG Universe
The first character to achieve Ascension in the mainstream Villains RPG Universe was arguably Arodnap during the climax of the Fall of Avalon - it has since become a regular trait of Arodnap and several other prominent antagonists of the Villains multiverse (though a few notable antagonists (such as the Voice) have never made use of such tactics).