The robots look like the actual Plankton. Excluding the robot in "Frozen Face-Off," the robots look metallic and have visible screws and metal plates.
Role in series
Plankton uses the robot as a decoy of himself in the sled race while he goes to the Krusty Krab to steal the formula. However, later on, SpongeBob and friends find out about the decoy after Patrick accidentally destroys the decoy by sitting on it.
The SpongeBob Movie: Sponge Out of Water
Plankton uses the robot as a plan B in case his tank robot fails; he switches places with a robot double that gives a fake penny to Mr. Krabs - with the real Plankton inside - and leaves the Krusty Krab sobbing. Later, when Mr. Krabs is gloating, he sees a loose thread on the robot and realizes that the real Plankton is inside stealing the formula.
"Goodbye, Krabby Patty?"
Plankton uses the robot as a decoy, sending it to Dullsville to retire, while the real Plankton tries to steal the secret formula. Plankton is stopped by Mr. Krabs and SpongeBob because they also sent robot decoys to the city. Meanwhile, at Dullsvile, the Plankton robot, Robot Krabs, and Robot SpongeBob talk about how they were used as decoys.
They become friends and hang out with each other until they explode.