The Flash Liquidizer Ultra Dousing Device, invented by Dr. Elvin Gadd, was found on Isle Delfino by Mario after being accused of vandalizing the island in the 2002 Nintendo video game Super Mario Sunshine. FLUDD is a backpack full of water and has a nozzle attached to the top, basically.

FLUDD has four basic modes: Spray, Hover, Rocket, and Engine. Spray allows Mario to spray a stream of water out ahead of him. Hover allows Mario to spray water beneath him, allowing FLUDD to be a kind of make-shift jetpack. Rocket fires a stream of water at high pressure, causing Mario to be propelled high into the air. Finally, as an Engine FLUDD fires out a constant stream of high pressure water that causes Mario to race along the ground (or water) at a high speed until either the water runs out or Mario collides with something.

FLUDD can only be equipped with two nozzles at any given time. The Spray nozzle is not interchangable, but the other three are. Rocket and Engine must be found on the island before they are available. Hover and Spray are available from the start of the game.

From time to time FLUDD will speak and give Mario advice, such as the weakness of a boss or the location of an item. He speaks with an electronic Stephen Hawking-type voice.