A Supermove is an ability than any playable character can use. Supermoves do not require any star rating or level, and cannot be upgraded. They can be performed by spending all 10 power bars.
Super moves have limitless range, and cannot be blocked. Additionally, each character can only use supermoves only once per match, afterwards they gain a 25% damage bonus for the rest of the match. Supermoves also transport the combatants to the center of the battlefield.
Doctor Fate's passive reduces power cost of any ability, including supermoves, by one bar. However, in the case of supermoves, all power is drained regardless, i.e. you could use it at 9 or 10 power bars, but you will be left with 0 power anyway.