Mercy was an alien from another planet. Having come to Earth, Mercy took it upon herself to kill those who lacked the strength to commit suicide from despair, believing that she was doing them a favor. Mercy was an enemy of the Hulk, as he was the only person Mercy was been unable to 'help'. No matter how bad things became, the Hulk would never stop fighting, because he must always be the strongest one there is.
Mercy has the ability to teleport to another area with a thought. She is able to read people's mind and has the power of levitation/flight. Mercy can create spears of energy which can kill a person. She is able to duplicate a person in form and personality.
In The Incredible Hulk: Ultimate Destruction, Mercy appears as the bodyguard for Emil Blonsky to get rid of gamma-irradiated beings. Unlike the comics, she isn't an alien from another planet. Like the comics, Mercy has the same powers of teleportation, telekenisis, and levitation except that she got her powers from gamma radiation, which was used as treatment that cured her of a slowly fatal brain tumor that would have eventually killed her. During her boss fight, Mercy plans to stop the Hulk from getting the fuel rods, but failed. As Mercy tries to tell the Hulk about her ex-employer's current plans, Blonsky kills Mercy as he blows up the building she was in to try and stop the Hulk.