After a magic show with Daphne volunteered, they head out at Atlantica in South America, but when the Ghost of Merlin returns, he starts to follow Mystery Inc. on a boat with shipments, and he uses a spinning transformation on Daphne, turning her into Ariel the Little Mermaid, and she heads into the sea remaining in the form forever. And now the gang must find a way to restore her to normal.
August 18, 1990 on ABC.
- Scooby-Doo (Don Messick)
- Shaggy Rogers (Casey Kasem)
- Fred Jones (Frank Welker)
- Daphne Blake/Ariel (Heather North/Jodi Benson)
- Velma Dinkley (Christina Lange)
- Merlin's ghost (John Stephenson) - revealed to be the sea captain
- 38-Year Old Ariel (Jodi Benson)
- 40-Year Old Eric (Christopher Daniel Barnes)