Unagi

Unagi is the Eel which inhabits Jolly Roger Bay, the third level of Super Mario 64. While it is not possible to defeat Unagi, he is needed to obtain two stairs from Jolly Roger Bay. It deducts 3 HP if you touch Unagi.

For the first star, Plunder in the Sunken Ship, Unagi is blocking the entrance to the sunken ship and needs to be lured away, allowing entrance. He returns to use in the second star, Can The Eel Come out to Play?. Again, you need to lure him out of his cave in order to obtain the star on his tail.