Plan Z is one of Sheldon J. Plankton's many plans to obtain the Krabby Patty secret formula and put the Krusty Krab out of business in The SpongeBob SquarePants Movie. It's the last plan under Plankton's disposal.
His plan was to obtain King Neptune's crown, frame Mr. Krabs, in which the punishment would be execution. As Mr. Krabs was frozen at first, and with SpongeBob on the journey to Shell City and Squidward enjoying his time off, no one was able to protect the secret formula, so Plankton stole it, and put the Krusty Krab out of business. Customers came to the Chum Bucket, in which he used to mind control them. He would then rule Bikini Bottom, and renamed it "Planktopolis". However, it was foiled by SpongeBob and Patrick making it to Shell City and back, and then Plankton was arrested and Mr. Krabs was freed, and Neptune got his crown back.
- Plankton called the file lemon-scented, possibly as a reference to E.V.I.L. (Every Villain Is Lemons).
- "Plan Z " is also the name of Adolf Hitler's plan for rearming the German navy prior to World War II (Kriegsmarine) so that it could matched up with the British Royal Navy on equal terms (the Kriegsmarine was a weak navy during Hitler's time). Unfortunately, war broke out in 1939 before the plan could be completed (theorized to be finished in 1947), and it fell apart in three years.
- A second Plan Z was formed in 1973 as a millitary coup to topple Chilean president Salvador Allende, though this was shown to be a fake as revealed by the CIA in 1999.