Gringill

Gringills are large, orange or lavender eel-like creatures with large eyes and teeth found in Super Mario Galaxy. They first appear in the Beach Bowl Galaxy and later appear in the Drip Drop Galaxy, Sea Slide Galaxy, Bigmouth Galaxy, and Deep Dark Galaxy. They can be defeated by throwing a Koopa Shell at them while underwater. They attack simply by trying to eat Mario. They may be the Super Mario Galaxy equivalent of Unagi. Some of them appear in caves, and come out a small distance when Mario/Luigi gets close.

They reappear in Super Mario Galaxy 2 in the Cosmic Cove Galaxy and the Starshine Beach Galaxy behaving like they did in the previous game.

Trivia

 * Their name is a portmanteau on "grin" and "gill."