One of my best on MS Paint. *sigh* OK, here's an explanation:

Momo's super form is triggered only when she feels extreme emotions of hatred. When this happens, she glows with immensive chaos energy.
And you know those black rings she wears? Those aren't there for decoration, as if you noticed thru Momo's various but not many outfit changes (she's had about 2,3 or 4) she always has those rings. When she turns UC the rings break from overload of chaos energy.
Yeah, they're LIKE Shadow's, but whenever she takes them off, she doesn't lose her power. If she takes them off when there is no fight, when she puts them back on later, her powers will be limited again. However, durig a fight her power goes up to infinity as long as she has the will to fight. After she turns back to normal, her powers are on empty and she loses conscienceness, then she goes into a 3 day coma so that she can restore her power back.

THERE YA HAVE IT!