- Billy (purple kid)
- Eugene H. Krabs
- Sheldon J. Plankton
- Incidental 13 (cameo)
- Incidental 37B (cameo)
- Incidental 40 (cameo)
- Incidental 41 (cameo)
- Incidental 45 (cameo)
In the beginning of the short, Mr. Krabs and Plankton are at the beach and they have finished building a sand castle. Thereupon, a bully fish named Billy points at his sand castle and says "This is a castle!" Billy shows off his fancy sand castle and then destroys Mr. Krabs' and Plankton's, saying that he is remodeling it.
Mr. Krabs and Plankton smile at each other and Billy wonders what they are all happy about. Suddenly, he gets launched into the air by a secret spring trap under the sand. Plankton states that bullies are predictable as the bully falls face down onto the sand, as the short ends.
|( ‣ ) Associated production music|
|( • ) Original music|
|( ◦ ) SpongeBob music|
‣ Moloka'i Nui A - Kapono Beamer [Plays throughout]
- This short is available on the Season 5 Volume 1, Complete Fifth Season, and Pilot a Mini-Movie and the Square Shorts DVDs.
- On the Pilot a Mini-Movie and the Square Shorts DVD, this short is listed as "Sand Castle - Swim Lessons."