The short starts with SpongeBob and Mr. Krabs at the Krusty Krab that is decorated for Halloween. Mr. Krabs gives SpongeBob a garbage bag filled with moldy sponges and tells him to take this bag out to the dumpster. On the way out, SpongeBob trips on a bucket. He and all of the moldy sponges were flying.
As SpongeBob is going to get out of the sponges, he sees the green moldy full moon. Because he is on the moldy sponges, he himself turns into Moldy Sponge for the rest of the short (which made him green and grow big eyebrows and mushrooms). Seeing that he turned evil, he laughs until he sees Mr. Krabs coming out of the Krusty Krab.
Mr. Krabs complains that he told SpongeBob to throw away the moldy sponges and that he has to do it himself. He takes SpongeBob and carries him into the dumpster, thinking that he is a moldy sponge. He groans about Mr. Krabs throwing him out, then the Halloween short ends.
( ‣ ) Associated production music
( • ) Original music
( ◦ ) SpongeBob music
‣Sailor's Sting 11 - Michael Bolger, Nicholas Carr [Krabs gives SpongeBob a bag of moldy sponges] ‣Danger HQ - Norman Dane [SpongeBob sees the full moon] ‣Dramatic Bridge 4 - Phil Green [SpongeBob turning green] ‣Sailor's Sting 11 - Michael Bolger, Nicholas Carr [Krabs puts SpongeBob in the dumpster]
The way SpongeBob transforms is similar to that of a werewolf.
When SpongeBob transforms, his shoes, socks, shirt, and hat turn green as well.