From the Super Mario Wiki
Dragoneels are gigantic sea serpents that make their debut in New Super Mario Bros. U. These enemies have angry closed eyes that resemble those of a Porcupuffer, and large spiny red jaws. Also, they have long sleek bodies with a long purple crest running along their red backs and their underside is white with pale purple polka dots, and a long pink fin along their back. Dragoneel's wing-like fins are similar to those of Cheep-Cheeps. They closely resemble Gobblegut (and Fracktail) and behave similar to the Snorkel Snake as they try to encircle players with their bodies.
Super Mario series
New Super Mario Bros. U
In the game, they attack by chasing the player's character. They can only be defeated with a star, and doing so causes it to spit out several coins. Dragoneels only appear in the Sparkling Waters level, Dragoneel's Undersea Grotto. It follows the player throughout the underwater course, while the players must avoid the monster. Throwing fireballs at its head will slow it down, but throwing them at its body will speed it up.
A purple-colored version of the Dragoneel called Baby Dragoneel also exists in the same level. They are shorter and make tighter turns, and are significantly slower. They only appear in a small location where a hidden Star Coin is found by going through a pipe.
New Super Luigi U
Mario Party 10
Dragoneel is a Chinese-like sea serpent. It has two wings coming from its neck, it is red with a beige underbelly. It has purple scales running down its body and has red jaws.
Names in other languages