F.L.U.D.D.

F.L.U.D.D. is the main deuteragonist of Super Mario Sunshine. He is  Mario's main ally throughout the game, and assists him in various ways. F.L.U.D.D. is originally invented by E. Gadd so Mario can use it to spray the graffiti all around Isle Delfino.

"Power-up complete. Thank you for purchasing this item from Gadd Science, Incorporated. Preparing to register customer information. Scanning and classifying subject data...subject identified as Mario, resident of the Mushroom Kingdom. Data storage complete. I am F.L.U.D.D., a Flash Liquidizer Ultra Dousing Device. I hope to be of assistance."

- F.L.U.D.D.

Super Mario Sunshine
In Super Mario Sunshine, F.L.U.D.D. can be used by Mario to spray water at objects or enemies by pressing R. By doing this, Mario is able to perform a multitude of tasks, ranging from enhancing his acrobatics to cleaning graffiti off of various surfaces. F.L.U.D.D. can switch between the Squirt Nozzle and either the Hover, Rocket, or Turbo Nozzle (depending on which one Mario currently has equipped) with X. As the player continues to spray water with F.L.U.D.D., the amount of water in its tank will gradually get lower. When its tank is completely empty, the player must enter a body of water and hold the R button, or collect a Water Bottle before any water can be sprayed again. Throughout the game, F.L.U.D.D. will also often give the player advice on how best to complete a certain task or challenge via a HUD message, which varies depending on the situation.

Mario first encounters F.L.U.D.D. on the ground of the Delfino Airstrip. When he walks over to F.L.U.D.D., it introduces itself to Mario before he puts it on; the player is then shown a tutorial video detailing how to use it. From this point on, Mario carries F.L.U.D.D. around on his back and has access to it throughout the rest of the game. However, there are certain situations in the game when F.L.U.D.D. will be unavailable to the player. For example, it is taken by Shadow Mario every time Mario enters a secret level that has not been cleared at least once. It is also taken by Shadow Mario in The Goopy Inferno|Episode 3 of Pianta Village, though in this case the mission involves finding a way around the iery Goop that covers the entire village and retrieving F.L.U.D.D.

After Mario defeats both Bowser and Bowser Jr. in Corona Mountain at the end of the game, Mario and Princess Peach fall through the air and land on a small island on the west side of Delfino Plaza. When Mario locates F.L.U.D.D., laying on the ground a few feet from him, it is shown to be damaged and malfunctioning, asking Mario if "[it] was of assistance" before it shuts down completely. Shortly after, at Sirena Beach, several of the Toads accompanying Mario and Peach to the island present to them F.L.U.D.D., who has been fixed.

Super Mario Galaxy / Super Mario Galaxy 2
Although F.L.U.D.D. itself does not appear in Super Mario Galaxy or Super Mario Galaxy 2, Water Shooters, Fire Cannons, and Electric Pressures, all of which resemble F.L.U.D.D.'s head, appear.

Super Mario-Kun
F.L.U.D.D. also appears in the Super Mario Sunshine adoption of Super Mario-Kun. As with F.L.U.D.D. in the games, it assists Mario, although it expresses more emotion and is more difficult to be with. It sprays Mario's face, causing Mario to yell at it, for example.

Mario Power Tennis
Several F.L.U.D.D.-like water pumps appear in Mario Power Tennis; these heads are used to clear away the Graffiti that can accumulate in the Delfino Plaza Court. Also, in the minigame Tic-Tac-Glow, the player must use balls of water shot by several F.L.U.D.D. pumps to clear away Goop in a tic-tac-toe like the game.

They also appear in the [Chain-Chomp Challenge, when a Chain Chomp begins chasing a player. Its purpose is to calm the Chain Chomp down when it's enraged.

WarioWare series
F.L.U.D.D. makes a small appearance in WarioWare: Smooth Moves in a Super Mario Sunshine microgame, in which it must be used to put out a building fire. The microgame later reappears in WarioWare Gold, where the F.L.U.D.D. is instead used to clean graffiti off the side of the building.

Mario Kart Arcade GP 2
F.L.U.D.D. appears in Mario Kart Arcade GP 2 as a "Water Spraying" item. When used, the item sprays water and if it hits a driver, they spin around similar to if they hit a Banana Peel.

Mario Kart Arcade GP DX
F.L.U.D.D. reappears in Mario Kart Arcade GP DX as an item. It acts the same as in Mario Kart Arcade GP 2, as a "Water Spraying" item.

Super Smash Bros. series
F.L.U.D.D. appears as Mario's down special move in Super Smash Bros. Brawl, Super Smash Bros. for Nintendo 3DS / Super Smash Bros. for Wii U] and Super Smash Bros. Ultimate, replacing the Mario Tornado from the previous games. When Mario uses the move, he will put F.L.U.D.D. on his back and douse his enemies with water. The attack does not damage opponents, but instead pushes them. F.L.U.D.D. charges when the move is activated and shoots water when the button is pressed again, a longer charge resulting in a more powerful stream of water. F.L.U.D.D. stops charging when it is fully charged, allowing Mario to use it at a later time. Mario can also shield or roll to stop the charging. Mario can destroy projectiles with F.L.U.D.D., and the stream of water can be angled.

In Super Smash Bros. for Nintendo 3DS / Wii U, the F.L.U.D.D. move has two custom variations. The first is Scalding F.L.U.D.D., which sprays a short-range stream of water that deals fire damage to opponents. The second is High-Pressure F.L.U.D.D., which sprays a more powerful stream of water and has greater range but also pushes Mario back.

When spraying water, F.L.U.D.D.'s nozzle is next to Mario's head on the right-hand side, while Mario holding a handle with his left hand and holding the nozzle with a right hand. However, In the original Super Mario Sunshine, F.L.U.D.D.'s nozzle is above Mario's head, with Mario gripping both handles with both hands.

Minecraft: Wii U Edition / Minecraft: Nintendo Switch Edition
In Minecraft: Wii U Edition and Minecraft: Nintendo Switch Edition, F.L.U.D.D. can be found in the miscellaneous section. The empty bucket has been replaced by F.L.U.D.D. with dark blue water, the water bucket is F.L.U.D.D. with light blue water, the lava bucket is F.L.U.D.D with lava and the milk bucket has F.L.U.D.D. with milk. The water bucket F.L.U.D.D. can be used to place water, the lava bucket F.L.U.D.D. can be used to place lava, and the empty bucket F.L.U.D.D. can be used to pick up running water and lava. The milk bucket F.L.U.D.D. can be used to raise the player's health bar and is obtainable by milking a cow. Mario with F.L.U.D.D. on his back is a playable skin.

Trivia

 * When F.L.U.D.D. scans Mario in Super Mario Sunshine, a little window in the bottom left corner shows short gameplay clips of various Mario franchise games, such as Super Mario Bros., Super Mario World, and Super Mario 64. After Bowser is beaten at the end of the game and F.L.U.D.D. is looking at Mario, the window shows the Game Over screen from Mario Bros. (game). In addition, in the bottom right corner, the titles of several other Mario games that Mario had been in up to and including that point are shown, though they are backwards with no spaces between the words, so they normally cannot be read by the player. The game titles as they are displayed when F.L.U.D.D. scans Mario are as follows: MARIO BROS, Super Mario Bros., Super Mario Bros. 2, Super Mario Bros. 3, Super Mario World, Super Mario Kart, Super Mario 64, Mario Kart 64, and Super Mario Sunshine ("KART" is misspelled "KIRT" in the game titles for Super Mario Kart and Mario Kart 64, which is likely due to a mistranslation of the kā syllable in their Japanese titles).
 * In Super Mario Sunshine during the cutscene at Pinna Park, F.L.U.D.D. is revealed to have the Gadd Science Inc. logo at the base of its nozzle. However, this is the only time F.L.U.D.D. is shown to have it present.
 * During development of Super Mario Sunshine, F.L.U.D.D. was List of Super Mario Sunshine pre-release and unused content planned to feature a water gun nozzle, but the idea was scrapped due to controversy in the United States at the time.