Gill-Man with other party-goers
Gill-Man is the Creature from the Black Lagoon.
The New Scooby-Doo Mysteries
Gill-man was one of the monsters in Dracula's party. (A Halloween Hassle at Dracula's Castle)
Intro
Gill-Man can be seen dancing with Frankenstein, Igor, Dracula, Wolfman, and Medusa.
Scooby-Doo And The Ghoul School
In the end, Gill-Man was seen with his daughter, Godzilla and his daughter, and the Fly with his daughter, but Scooby and Shaggy had enough so they left.