Sandy-Plankton relationship
Sandy and Plankton have had very few interactions during the series. Their first interaction is in "Someone's in the Kitchen with Sandy" when Plankton steals Sandy's fur in order to trick SpongeBob into giving him the Krabby Patty secret formula. This fails when Sandy comes into the Krusty Krab and tries to beat Plankton up to get her fur back, which also fails and ends up with Sandy going to jail.
Their second interaction is in "Perfect Chemistry," when Sandy and Plankton team up, but what Sandy didn't seem to know is that Plankton was using her to get the Krabby Patty secret formula though she actually did. Sandy claims that she knew Plankton was going to trick her all along and sent Plankton to be trapped in Mr. Krabs' Krabby Patty secret formula bottle after yet again failing to get it to foil his plan.
They did not interact much until "Squirrel Record," when Sandy wants to break all records, including eating the most chum, and Plankton warns her that the chum is raw before eating it.
"It Came from Goo Lagoon," where SpongeBob, Patrick, and Sandy team up to defeat Plankton. They soon find Mr. Krabs and Plankton being rude to one another until Mr. Krabs yet again wins.
"Salsa Imbecilicus," where Sandy accidentally gives Plankton an evil plan to steal the recipe. Plankton fails with his plan and gets himself caught in Patrick's DNA making by accident. Sandy and Karen team up to help Plankton and the rest of Bikini Bottom.
In "Mimic Madness," they are seen playing chess together and teamed up to get rid of SpongeBob's Mocking Mimicry Madness.
In "Plankton Paranoia," she, along with the rest of the gang, secretly team up with Plankton to help put Mr. Krabs' mentally insane behavior to a stop because it was ruining the restaurant business. To do that, they planned an anniversary party of when Plankton first tried to steal the secret formula, which turned out to be a success.
In "Girls' Night Out," Karen, Sandy, and Mrs. Puff do prank him into dressing up as Mr. Krabs by telling him Mr. Krabs will give the Krabby Patty Secret Formula. Later, in Sandy's treedome, he and Mr. Krabs fight as amoebas ruining Mrs. Puff's, Karen's, and Sandy's relaxing.
In "Mad Science Squirrel," Plankton recruits Sandy to work in her lab, with the intention of using her to make a machine to harm Mr. Krabs. Instead, Sandy renovates the machine to do harmless things, frustrating Plankton.
In "Parasite Pals," Sandy forces Plankton to remove the parasite from SpongeBob's body, because it was the food Plankton cooked that made him sick.
"Plankton's Special Sinister Commentary" has him calling Sandy a "do-good" and mentioning she's going to ruin everything. This is related to Plankton's hope of Mr. Krabs disappearing in the "SpongeBob SquarePants vs. The Big One" special.
In "Plankton: The Movie", Sandy, along with Mrs. Puff and Pearl, scold Plankton for his abuse towards Karen and for triggering her transformation into a monster in the first place. They interrogate him on what caused her transformation through SpongeBob's hypnosis watch where they've learned that she removed her empathy chip in the fit of her rage. They tell Plankton that the only way to set things right is to simply apologize to her. But apologizing is something Plankton finds it hard to do. So, Sandy installs the empathy chip into his brain to make him realize the error of his mistakes. She then helps Plankton infiltrate Mega Karen so that he could reach Karen and apologize to her before she could reach the surface.
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