The robots look like the actual Plankton. However, if one sits on Plankton or peel his skin off, one will reveal that it is a gray robotic dummy version.
Plankton used the robot as a decoy of himself in the sled race while he went to the Krusty Krab to steal the formula. However, later on, SpongeBob and the gang found out that he was a robot and that the real Plankton was trying to steal the formula.
The SpongeBob Movie: Sponge Out of Water
Plankton used the robot as a plan B so if his Giant Robot failed, he would switch places with a duplicated robot of himself that would give a fake penny to Mr. Krabs with the real Plankton inside and leave the Krusty Krab sobbing. Later, when Mr. Krabs was gloating, he saw a loose thread on the dummy and realized the real Plankton was inside stealing the formula.
Plankton used the robot as a decoy which went to Dullsville to retire, while the real Plankton when to steal the secret formula. Plankton got stopped by Mr. Krabs and SpongeBob because they sent robot decoys to Dullsville as well. Meanwhile at Dullsvile, the Plankton Robot, Robot Krabs, and Robot SpongeBob talk about how they are used as decoys. Later, they enjoy their holiday with each other until they explode.