This article contains speculative information. Please keep this in mind as you read it.
When SpongeBob met Plankton, he tried to befriend him, but as Plankton told him that he wants a Krabby Patty (& by extent, the formula), SpongeBob refused. 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 told SpongeBob to stay away from Plankton as he tries to steal the formula. As Plankton told SpongeBob of his ambitions, SpongeBob tells him that he'll never get a Krabby Patty. Plankton then hijacks his brain & controls him to the Krusty Krab to get a Krabby Patty & haul it to the Chum Bucket. As SpongeBob was controlled into dropping it to the analyzer, he apologizes for his actions to describing the tasty qualities of the Krabby Patty, causing Plankton to exit him & attempt to gain the Patty, only to be dropped to the analyzer. As SpongeBob leaves the Chum Bucket with the Patty, Plankton yells at SpongeBob to come back with the Patty.
- The SpongeBob SquarePants Movie: As Plankton framed Mr. Krabs for stealing Neptune's crown, SpongeBob & Patrick tried to retrieve the crown. Plankton then hires Dennis to assassinate the two. SpongeBob wasn't aware of Plankton's schemes until Dennis accidentally told 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 rock-'n-roll power to free everyone, & after being stomped on, Plankton gets arrested.
Episodes as friends
- F.U.N.: As the townsfolk ran him out of town, SpongeBob felt bad for Plankton & decided to befriend him. While he was reluctant at first, Karen told him of the mission to where Plankton changed his mind. Plankton refused to join along with SpongeBob's jolliness at first, but eventually decided to join him. Krabs sought sight of this. The next day, Plankton went in to the Krusty Krab for SpongeBob, but Mr. Krabs tried to tell SpongeBob that Plankton's not his friend. SpongeBob refuses to believe Mr. Krabs & leaves with Plankton. But after getting a Krabby Patty out of Plankton's pocket, SpongeBob languishes from this & begs Plankton the truth. Afterwards, Plankton leaves with the patty stating that being evil is just too much fun.
- Band Geeks: As the rest of the Bikini Bottom Super Band sung Sweet Victory, there was a scene where both SpongeBob & Plankton sung together.
- Plankton's Pet: SpongeBob agreed to help Plankton find a pet, eventually finding Spot in the process. Soon, as Plankton lost Spot, SpongeBob agreed to help find him. As they search at the animal shelter, SpongeBob accidentally opens the pens. Plankton then thanks SpongeBob for helping him, & as they were about to get mauled, SpongeBob noticed Spot hiding in Plankton's eye. As Spot saved them, SpongeBob was proud at this, with Plankton stating that he taught him everything he knows.
- The SpongeBob Movie: Sponge Out of Water -