Phoenix is a supervillain and an enemy of the X-Men. She was formerly known as Jean Grey, but became the Phoenix after her powers became too much to control. She still has the same powers, but given her current form, she's probably a lot stronger now. At one point, she gets corrupted into an even darker and more destructive form of herself known as the "Dark Pheonix". She also appears in Marvel vs. Capcom 3: Fate of Two Worlds.