- Eugene (debut)
- Eugene's parents
- Mayor Ethel Mermaid
- Ms. Snail
Names in other languages
|Spanish||"Un turbio misterio en Mermaidos" (Cyberchase Online listing)||"A Murky Mystery in Mermaidos"|
- This is the first episode that begins with "M" (articles not included) since the fourth season episode, "Measure for Measure".
Community content is available under CC-BY-SA unless otherwise noted.