One of the most direct examples of this trope is The Ghost of Plankton. Here, Plankton fakes his own death to possess Mr. Krabs’ body. While not physical time travel, the episode involves a séance and flashbacks that act as narrative time travel. Plankton drags SpongeBob through a literal memory lane—showing the past of Bikini Bottom.
This episode is crucial because it highlights the emotional stake of time travel. Plankton wants to go back to the moment he lost the formula. SpongeBob wants to go back to the moment he first blew a bubble. Their conflicting desires for the past destroy the séance machine, proving that you cannot rewrite history without a consensus.
They reappear in Sandy’s treedome just as they left. Plankton secretly deletes his memory of the future’s loneliness but keeps the memory of SpongeBob’s kindness. He mutters, “Next time, SpongeBob… next time.”
SpongeBob smiles. “Looking forward to it, Plankton!”
Sandy confiscates the Chrono-Key, but not before Plankton uses a tiny hidden backup to jump one minute into the future—just to steal a single Krabby Patty, which he eats sadly alone… but with a small smile.
The frequency of time travel in the series has had lasting effects on the continuity of the show:
Alternate-futures comedy (Two-part episode)
Time loop gag (Short/mini-episode)
When Plankton accidentally activates a stolen time-travel device, he drags SpongeBob along on a chaotic trip through Bikini Bottom’s past, present, and future—only to learn that messing with time might cost him the one thing he really wants.
The most popular fan theory regarding SpongeBob and Plankton time travel involves the origin of the Krabby Patty secret formula. Consider this: Plankton has tried every trick in the book to steal the formula. He has failed thousands of times. What if, in one timeline, he finally succeeded?
The theory posits that in a deleted/unproduced storyline, Plankton builds a working time machine and forces SpongeBob to operate it. They go back to the day Mr. Krabs invented the formula. But upon arrival, they discover that there is no formula. Mr. Krabs just uses love, or mayonnaise, or something intangible.
A desperate Plankton tries to steal "nothing," but SpongeBob, wanting to help, accidentally gives young Mr. Krabs a slip of paper with a recipe for "Chum on a Bun." Mr. Krabs laughs, throws it away, and writes his own recipe. That slip of paper fossilizes, and millions of years later, Plankton digs it up, believing it’s the original formula—hence his lifelong obsession. SpongeBob created Plankton’s obsession through time travel. It’s a perfect Bootstrap Paradox.