From the Super Mario Wiki
Jumbo Rays are a type of stingray that appear first in New Super Mario Bros. Wii. These rays are green and wear a pair of water goggles. They have the ability to leap and fly through the sky, so Mario and company can stand on them as platforms until they disappear into the fog. Their appearance and manner are similar to those of Dolphins.
New Super Mario Bros. Wii
Jumbo Rays appear only in World 5-5 of New Super Mario Bros. Wii. Here, Mario and company must use them to traverse the level. Jumbo Rays make a noise when the player jumps on them similar to when the player jumps on a Parabeetle. However, the Jumbo Rays' sound does not go up the music scale as the Parabeetle does.
Mario Kart Arcade GP DX
Mario Party: Island Tour
A large group of Jumbo Rays can be seen in the background of the Hot-Air Hijinks minigame mode of Mario Party: Island Tour. Another one can be seen in the background of one of the scenes depicted in the minigame Get Reel.