From the Super Mario Wiki
Wind Duppies (also known as Cloud Duppies) are a species of enemy that appear only in Super Mario Sunshine. When Mario is on a high place, a Wind Duppy forms. It first spins around Mario then suddenly stops and charges Mario. If it hits him, Mario usually gets knocked off the platform. They can be temporarily dispatched using F.L.U.D.D., and defeated using Yoshi's tongue. Wind Duppies yield a single coin upon defeat.