Plankton's Death Ray just appears in the episode: Tentacle-Vision. As the name says it, it belongs to Plankton. Plankton shoots at Mr. Krabs with this ray in the TV series, Squidward Chat. It is seen again at the end of the episode, where Plankton uses it again to shoot at Mr. Krabs while in the show Squidward's House Party.
The death ray is blue with yellow and red stripes.