Unagi

The Unagis are a species of eels that first appeared en masse during the events of New Super Mario Bros. (although the first known Unagi was Super Mario 64's Unagi the Eel). Their name comes directly from the Japanese word for eels, 「うなぎ」 (Unagi). During some underwater levels, Unagis would swim around in a predictable pattern trying to hit Mario or Luigi. Some Unagis also live in small underwater coves, attacking anything in its vicinity. There is also a subspecies called the Mega Unagi.

Several Unagis reappear in Mario Kart Wii, where they can be seen while traveling through the underwater tunnel in Koopa Cape, poking their heads out of various Pipes. Another, perhaps a Mega Unagi, can be seen swimming outside of Chain Chomp Wheel.

They also reappear again in Mario Kart 7, making a cameo in the underwater zones of Daisy Cruiser and Koopa Cape. In Mario Kart Arcade GP DX, they appear in the underwater parts of the race track Tropical Coast.

A single Unagi appears an underwater section of the Mario Kart 8 track, "Dolphin Shoals".