It's Shadow Mario! After Him!
From the Super Mario Wiki
It's Shadow Mario! After Him! is the seventh episode of Gelato Beach in Super Mario Sunshine. The episode's objective is to chase down and defeat Shadow Mario and it is the third of seven episodes that involve doing so.
Shadow Mario will be waiting for the player on the beach, and he will begin running toward the back of the beach once the player gets near or sprays him from a distance. Shadow Mario will only run around behind the tower and the hills above. He'll Wall Jump up to the hills, run past the plaza area, and slide back down to behind the tower in a loop. Continuously spraying him by lightly pressing until he falls will reward the player with the Shine Sprite.
Names in other languages