Ghostfreak

Ghostfreak is a shadowy alien with the power to go trhought walls and turn invisibble. He can also rip away his skin to reveal a lot of tentaceles that are very strong. Ben first used Ghostfreak in permanent retirement and then lost the form in Ghostfreaked Out. He regained Ghostfreak in Be Afraid of the Dark but in the natural sun-weakened version, not with the protective skin, making it debatable if he is considered an original alien or a new alien.