King Neptune's crown, unlike his one from the regular episodes, is red and golden with a fishbowl-like shape.
Role in movie
King Neptune greatly cares for his crown mainly because it covers his bald spot. He even has a royal crown polisher to polish the crown and tries to have him executed just for touching it. Fortunately, Princess Mindy lets the polisher go much to King Neptune's fury.
Later, Plankton steals King Neptune's crown and blames it on Mr. Krabs as part of his Plan Z scheme. Neptune then heads for the Krusty Krab to confront Mr. Krabs about his crown. However, when Krabs says he does not have it, King Neptune shows a picture of Mr. Krabs saying he has stolen it. It does not help Krabs much when someone on the phone calls thanking Mr. Krabs for selling him the crown which is now in Shell City.
King Neptune is furious to hear that his crown is at Shell City and prepares to execute Mr. Krabs. However, SpongeBob steps in and agrees to get the crown back for him. King Neptune is later convinced and allows SpongeBob six days to get back the crown. SpongeBob and Patrick then set out to Shell City to retrieve the crown.
They go through many trials throughout their journey. They are eventually captured by the Cyclops and are taken to Shell City. Knowing where they are at, SpongeBob looks over to see King Neptune's crown, which is being sold for $7.00. SpongeBob and Patrick then dry up on the table, accepting their fate. Fortunately, their tears allow the sprinkler system inside Shell City to turn on and revive them. As the other revived creatures attack the Cyclops, SpongeBob and Patrick take the crown and leave Shell City.
On dry land, David Hasselhoff appears and agrees to give SpongeBob and Patrick a lift. Back at Bikini Bottom, as King Neptune prepares to kill Mr. Krabs, Hasselhoff fires SpongeBob, Patrick, and the crown down to the Krusty Krab, where it deflects King Neptune's blast onto Hasselhoff.
Neptune is happy to get his crown back but Plankton soon controls him with one of his Chum Bucket bucket helmets. SpongeBob soon does a monologue about his journey before bursting out into song and destroys all of the bucket helmets.
Mindy then gives back the crown to King Neptune and Plankton is soon arrested for framing Mr. Krabs.
Role in series
Outside of the movie, King Neptune's crown has also appeared once in the series. In the episode "Lost and Found," the crown makes a cameo among the many items placed on the Lost and Found's shelves.