When SpongeBob meets Plankton, he tries to befriend him, but as Plankton told him that he wants a Krabby Patty (and by extent, the formula), SpongeBob refuses. From that point on, whenever Plankton tries to steal the formula or a Krabby Patty, most of the time, SpongeBob tries to stop him. However, despite this, they have been friends a few times.
Episodes as enemies
- "Plankton!:" Mr. Krabs tells SpongeBob to stay away from Plankton, as he tends to try to steal the formula. As Plankton tells SpongeBob of his ambitions, SpongeBob tells him that he will never get a Krabby Patty. Plankton then hijacks his brain and controls him to the Krusty Krab to get a Krabby Patty and haul it to the Chum Bucket. As SpongeBob is controlled into dropping it into the analyzer, he apologizes for his actions to describing the tasty qualities of the Krabby Patty, causing Plankton to exit him and attempt to gain the patty, only to be dropped into the analyzer. As SpongeBob leaves the Chum Bucket with the patty, Plankton yells at SpongeBob to come back with it.
- The SpongeBob SquarePants Movie: As Plankton frames Mr. Krabs for stealing King Neptune's crown, SpongeBob and Patrick tried to retrieve the crown. Plankton then hires Dennis to assassinate the two. SpongeBob is not aware of Plankton's schemes until Dennis accidentally tells them. During the climax, SpongeBob then confronts Plankton, only for Plankton to mind-control King Neptune. As SpongeBob lays defeated with Plankton mortifying him as a "kid," he uses his Goofy Goober guitar to free everyone, and after being stomped on, Plankton gets arrested.
Episodes as friends
- "F.U.N.:" As the townsfolk run him out of town, SpongeBob feels bad for Plankton and decides to befriend him. While he is reluctant at first, Karen tells him of the mission as to where Plankton changed his mind. Plankton refuses to join along with SpongeBob's jolliness at first, but eventually agrees. Mr. Krabs sought sight of this. The next day, Plankton goes in to the Krusty Krab for SpongeBob, but Mr. Krabs tries to tell SpongeBob that Plankton is not his friend. SpongeBob refuses to believe Mr. Krabs and leaves with Plankton, but after getting a Krabby Patty out of Plankton's pocket, SpongeBob languishes from this and begs Plankton the truth. Afterwards, Plankton leaves with the patty, stating that being evil is too much fun.
- "Band Geeks:" As the rest of the Bikini Bottom Super Band sing "Sweet Victory," there is a scene where both SpongeBob and Plankton sing together.
- "SpongeBob Meets the Strangler:" Plankton goes to two parties for SpongeBob.
- "Plankton's Pet:" SpongeBob agrees to help Plankton find a pet, eventually finding Spot in the process. Soon, as Plankton loses Spot, SpongeBob agrees to help find him. As they search at the animal shelter, SpongeBob accidentally opens the pens. Plankton then thanks SpongeBob for helping him, and as they are about to get mauled, SpongeBob notices Spot hiding in Plankton's eye. As Spot saves them, SpongeBob is proud of this, with Plankton stating that he taught him everything he knows.
- The SpongeBob Movie: Sponge Out of Water: SpongeBob and Plankton team up to save the Krabby Patty formula.
- "Plankton Gets the Boot:" SpongeBob happily allows Plankton to take residence in his house after the latter gets kicked out by Karen, and later tries to help him win back Karen's heart.