Phantamanta

"This giant manta-shaped thing showed up. It was this paper-thin...floating silhouette. It came and covered the hotel grounds in this electric goop."

- Hotel manager

Phantamanta, originally known as the Manta,  is a boss who appears in the first episode of Sirena Beach in Super Mario Sunshine. It is the cause of Hotel Delfino's disappearance. It is a pale salmon-colored silhouette of a manta ray. When Mario sprays it with water from FLUDD, it splits into smaller versions of itself, also referred to as Manta rays. It possesses the uncanny ability to project itself over any surface of varying elevations instantaneously, much like a shadow.

Wherever the Manta moves, it leaves a trail of teal-and-yellow electric goop, which Mario can spray with FLUDD. If there is even a tiny drop of it left, Mario can get zapped when he touches it. The Manta cannot reach Mario if he is under one of the two huts or under a coconut tree, which is foreshadowed by a Pianta in one of the huts if Mario speaks to her before the battle. If the Manta is still in its largest form, it can still hurt Mario under the huts or trees. In addition, if Mario stands in the water, the Manta can still reach him, but it cannot produce goop with a shock. Upon contact with FLUDD's water, the Manta first divides into two. Each of those Mantas can divide into three more. Each of those divides into four Mantas. Lastly, each of those can further divide into four more Mantas, making a total of 96 Mantas to defeat. When all of the Mantas have fully divided, they turn pink, become irate, and start swarming towards Mario; until this point, the smallest Mantas do not pursue him, but all the larger sizes do. Once the last one is vanquished, Hotel Delfino is restored, revealing a Shine Sprite for Mario to collect.

Trivia

 * The Manta's music is a slightly eerie remix of the boss music that plays when the player fights the Plungelos, the Gatekeepers, and Gooper Blooper (in Noki Bay's second episode).
 * The goop that the Manta leaves behind before Mario arrives is in the shape of the Manta itself.
 * The Manta may have been inspired by the ending of the horror novel , after the Overlook Hotel is destroyed: "For a moment it assumed the shape of a huge, obscene manta, and then the wind seemed to catch it, to tear it and shred it like old dark paper. It fragmented, was caught in a whirling eddy of smoke, and a moment later it was gone as if it had never been."
 * In Mario Golf: Toadstool Tour and Mario Golf: Advance Tour, one of the default names on the scoreboards is Phantamanta, which is a pun on "phantom" and "manta."
 * In Splatoon 3, Big Man's boss fight pays homage to Phantamanta, with the ink color even being identical to the goop Phantamanta uses. His boss title, "The Hype Manta Storm," also references The Manta Storm, the name of the mission in which Phantamanta is fought.