Geronimo Stilton (2009)

S01E25 Smarty Pants

Geronimo, overwhelmed with commitments, asks his cousin Trap to participate in an intelligence experiment on his behalf. However, when Trap comes back, he’s transformed—intelligent and insufferable. Now, Geronimo and his friends must find a way to revert Trap to his former self quickly, or risk losing the Trap they know forever.