The Manta or Manta Ray is a character from Super Mario 64 and its remake. It resides in the level Dire, Dire Docks, where it swims in a circle around the whirlpool in the center of the entrance area. The Manta will leave a trail of shimmering rings as it swims around the whirlpool.
Mario should keep his distance from the Manta’s tail, as it can deal damage.
by Mastermind777, info from Super Mario Wiki