History
The Mento-Helmet's purpose was to intensify Professor X's brain waves and make them even more powerful than they normally were.[1]. He used it to mentally pinpoint Lucifer at one point, before being attacked by him.[2] Later, Marvel Girl used it to probe Professor X's subconscious after an experiment involving the Juggernaut went wrong. In the process, she managed to uncover the secret origins of the Crimson Gem of Cyttorak.[3]