Silhouette was an Mesypnomer from Encephalonus 1. He was thrown out of The Plumber (Ethereal) for taking alien techs and selling it. Silhouette was sent to Psychic Zone by Reinsarrig 3. In Seventh Heaven, he tries to steal the godly apples of Idunn to become immortal. Silhouette became immortal and sold the godly apples to under-covered Ben. Ben and Silhouette fought. In My Omnitrix, Mindmesser was deleted from Omnitrix after Silhouette took it (in fact Silhouette stole Omnitrix of Courtney).
Go to Mindmesser
He will return in "Ultimate Omnitrix 2".