Scooby and the gang investigate an abandoned ship, where it was all a ruse about a sea kraken, as Merlin's ghost returns casting an enchantment on Daphne, using a spinning transformation to turn her into Ariel the Little Mermaid, and maniac fish hookers to try and go out for the amnesiac Daphne, who believes herself to be Ariel, and the Guys and the N decide to help restore Daphne back to normal.
- Scooby-Doo (Frank Welker)
- Shaggy Rogers (Matthew Lillard) - is shocked to see Billy-Bob Scroggins trying to kill him again, even worse, Sadie-Mae Scruggins trying to smooche him again, much to the jealousy and cluelessness of Velma
- Fred Jones (Frank Welker)
- Daphne Blake/Ariel (Grey DeLisle/Jodi Benson) - was transformed by the ghost of Merlin
- Velma Dinkley (Mindy Cohn) - is jealous that Shaggy may have a relationship with Sadie-Mae
- Guys and the N:
- Kyle Tennyson (Jesse McCartney)
- Derek Kain (Adam Wylie)
- Roderick Johnson (Ogie Banks)
- Jerry Lewis (Adrian Truss) - the Guys and the N's superior
- James Duran (Robin Williams) - the kind mayor of Grobor, who hasn't seen his wife after her pass away
- Sadie-Mae Scruggins (Tara Strong) - Shaggy's old crush since Scooby-Doo and the Boo Brothers
- Billy-Bob Scruggins (Jason Spisak) - Shaggy's assassin since Scooby-Doo and the Boo Brothers, Reason: wants to get back at Shaggy for getting close to Sadie-Mae
- Leslie Wilkins (Maurice LaMarche) - The sheriff of the town, he has a hat, a mustache, Reason: he held Shaggy and Scooby at gunpoint and to make them burry their own graves, so he can purchase Daphne/Ariel
- Max Luke (Logan Grove) - the snobbish 11-year old boy, who Derek hates, Reason: he scared Kyle and Derek with a fake wizard voice
- Zarko (Corey Burton) - Reason: he must've had something to do with Daphne's transformation
- James Duran (Robin Williams) - his wife's wedding ring was found in a lettuce, which Kyle and Scooby found, he was the speaker of the wizard, Reason: To teach the Sheriff a lesson, and stop the feuds.
- Max Luke (Logan Grove) - Reason: To get the money.
- This is the third crossover with Disney.