From the Super Mario Wiki
Gringills are large
eel-like enemies in
Super Mario Galaxy. They have large eyes and teeth, and can be orange or lavender in color. 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 killed by throwing a
Koopa Shell at them, while underwater. They attack simply by trying to eat
Mario, similar to
Bubba from
Super Mario 64. 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.
