Gringills are , orange or brown eel-like creatures with large eyes and teeth found in Super Mario Galaxy. Their name is a portmanteau on "grin" and "gill". There are two variants of Gringills; smaller ones, which can be found swimming around freely or hiding in caves in certain galaxies, and larger variants, which solely lurk in caves.
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 attack simply by trying to bite Mario. Gringills can be defeated by throwing a Koopa Shell at them while they are underwater. Most of them appear in caves, and they come out a small distance when Mario/Luigi gets close, though rarely they are seen outside their holes, swimming in circles. There are also huge Gringills that are brown in color, have darker stripes, have two feelers on their lower jaws, and are found only in caves. They make a straining noise when coming out of their holes, and give a 1-Up Mushroom when defeated. These huge eels only appear in the Beach Bowl Galaxy, Sea Slide Galaxy, and Deep Dark Galaxy.
Both sizes reappear in Super Mario Galaxy 2 in the Cosmic Cove Galaxy, the Starshine Beach Galaxy, and the Slimy Spring Galaxy. They are only seen hiding in caves, and are no longer seen swimming outside of it.