Several Unagis in New Super Mario Bros. DS.
Unagis are enemies that appear in Mario Kart Wii. They can be seen traveling through the underwater tunnel of Koopa Cape, some poking out their heads out of various underwater Warp Pipes. A Mega Unagi can be seen swimming outside of the Chain Chomp Wheel. Unagis cannot harm players in Mario Kart Wii, because their area is inaccessible, but in other games such as New Super Mario Bros. (DS), they can harm the player when he comes in contact with them.
