Rage can occur when one has intense anger. In mutant, this causes a problem. When they go into rages, they sometimes lose themselves, but gain extra power. Wolverine has been known to go into a rage and have a large amount of strength at his disposal. Other mutants might go into rages where they are emotionally strained where their powers are lost to them. The effects of rage differ from mutant to mutant.
Note: This is less a power than an effect that might enhance or be a detriment to a mutant's powers or control over those powers.