It's a blaster-like gun that is mostly light blue. It has a yellow handle and a red trigger. It also has a pattern of yellow rings.
Role in episode
After seeing what Mr. Krabs, Sandy, and Pearl are doing on Squidward Chat, Plankton claims he can cause more collateral damage than all of them. He gets on the show and shoots almost everything in Squidward's house, even Mr. Krabs.