He is a green metal fish in a purple metal suit. He wears a black top hat with a white stripe around the bottom. Before he enters the Krusty Krab, he puts on a fake mustache.
He enters the Krusty Krab to tell SpongeBob that he will win a million-dollar bill if he reveals the Krabby Patty secret formula. After SpongeBob says that discussing the formula is forbidden, Plankton jumps out of the disguise to intimidate SpongeBob, getting caught by Mr. Krabs in the process.