Killjoy is a daranged psychopath who's mind was warped when his head was severley burned.
Although not a mutant when Killjoy was human, he was a scientist and worked with chemicals and technology. All that is known is that a science experiment gone wrong exposed his skull and twisted his mind. But the chemicals he was exposed to gave him amazing acrobatic skills and heat vision.
Despite being completely insane, Killjoy is a genius and has an amazing knowladge of gadgets and technology, resulting in him managing to create a suite with an arssenal of deadly weapons at his disposal. He uses bombs, blades, guns, basicly anything that will spread mayhem and destruction. Thanks to his chemical exposure he is incredably acrobatic (despite the heavy suite) and can emite beams of heat from his eyes (or what's left of them) With his suite on, Killjoy possesses super-human strength and hand blasts.