It is a small crane that is designed as a white and red boat with black tracks under it with a crane with a purple fist resembling the one seen at the top of the Chum Bucket attached to the front boat.
Role in episode
Plankton plans on using his crane in order to help build the Mega Bucket on Goo Lagoon. However, this proves difficult due to the Bikini Bottomites getting in his way and not listening to his threats.
Plankton manages to trick SpongeBob into driving away all of the Bikini Bottomites by teaching him assertive behavior. Plankton then uses his crane to carry the fist for the Mega Bucket. SpongeBob realizes that Plankton used him, and puts a stop to this by being nice and bringing all of the Bikini Bottomites back to Goo Lagoon.