Elliot was thought to have killed his parents when his mutant powers first emerged. Their deaths lead to Nick Fury taking the boy to Xavier's to be observed and trained in the use of his abilities. Elliot quickly worked his way into the core group of the X-Men and even joined in a mission to the Academy of tomorrow where the Brotherhood attacked during the school dance.
During his absence from the mansion, Nick Fury talked to Xavier about taking Elliot "Magician" into SHIELD custody. Xavier informed Fury of how Elliot arrived at the mansion and that the scope of his power has been revealed. Upon arrival of the group Xavier informed the team of Elliot's actions and the team attacked Elliot. During the fight Elliot exhibited more of his power by creating instances of Multiple Man, Blob, and Toad of the Brotherhood to attack the X-Men. At the conclusion of the battle Wolverine drove his claws into Elliot's chest, presumably causing his death.
At the end of the day Elliot is shown talking to Kitty about his power and potential and that he was not really dead, but chose to disappear and try to learn control of his abilities. This was done only for personal reasons as Kitty never actually saw or heard Elliot.
Magician's mutant ability enables him to alter reality. He can create people or objects that were previously not present, resist the psionic abilities of others, manipulate gravity and other natural forces, and manipulate the memories of those around him. He can give himself super strength and can seem to locate people even though he doesn't know exactly where they are. He has been seen to trap the entire X-men team in the ground while fighting Phoenix(Jean Grey), Nick Fury, and Professor X. He has even erased the memories of the entire X-men team including Professor Xavier, who is supposed to be the most powerful telepath on Earth. Elliot's powers also seem to be at least partially driven by his unconscious desires to see certain events made into reality.