Space Dandy

Scarlet becomes fed up with the costs of paying Dandy's bounties for petty aliens, and challenges him to capture a Chameleonian, a rare alien with the ability to mimic any creature or object's appearance. The Aloha Oe crew unknowingly happen upon the creature on a fishing spree and bring their catch aboard their ship, where it begins impersonating the crew to outwit them and evade capture. Eventually the crew encounter the Chameleonian in the form of Dandy and, unable to tell the real Dandy apart from the impostor, put them through a series of questions only Dandy can answer. However, the Chameleonian becomes so adept in acting like Dandy that it comes to truly believe itself to be him, making the two indistinguishable. The Chameleonian stays with the crew in Dandy's form until it is caught by Dr. Gel and impersonates him, causing the doctor to succumb to Gestaltzerfall as he questions who he is, and leaving QT and Meow to ponder whether the remaining Dandy is real or not. (Source: Wikipedia)