Also why not make Stand Power a type of Overdrive that will give you usage to ult moves, but decrease your Energy gain? Also some buffs for a character in Stand power.
I think infinite mana is enough of a buff. But yes I wanted to add an Ultimate Move after activating Stand Power that would end it immediately after using it. That would give you the extra strategy element of "Do I want infinite mana or do I risk using an ult and hope it will hit"