King Boo

King Boo is the leader of the Boos. He appears in Luigi's Mansion as the main enemy, he was sinister, clever, and determined. He has also made appearances in Mario Kart DS and New Super Mario Bros.. His powers include causing objects to appear out of thin air, breathing fire, shooting ice, strong tornado like breath, and the ability to jump incredibly high. He released all of the portraits' ghosts and trapped Mario behind a painting.

King Boo also appears in Mario Kart: Double Dash!! and Mario Kart Wii as an unlockable racer. In Double Dash!! he teams up with Petey Piranha.

Luigi's Mansion
In Luigi's Mansion Luigi wins a mansion from a contest he did not even enter or think about entering, but anyway invites Mario over. Mario wanders on alone and King Boo later catches him and traps him in a painting. Luigi, in the meantime, has no clue that the mansion is haunted or Mario is kidnapped. Later, after encountering a group of ghosts, Luigi meets a professor named Professor E. Gadd who gives him the Poltergust 3000 and tells Luigi he freed all of his Portrait Ghosts. Luigi then sets off to save Mario, but later on ends up in a storage room and frees all 50 boos and King Boo himself and Luigi obtains a Boo Radar for his Game Boy Horror. Halfway through his quest Luigi discovers where King Boo has been keeping Mario and sets off to find the key to his room. At the final battle with King Boo he gets a giant mechanical Bowser suit to help him battle Luigi and the player must defeat him by tossing a spike ball at Bowser's head and then sucking up King Boo like a regular Boo. Afterwards, King Boo is defeated, Mario is rescued and King Boo ends up in a portrait.

Super Mario Sunshine
King Boo returns again in Super Mario Sunshine in which he is the boss of episode five of Sirena Beach. To reach him the player must head to the casino and ground pound a purple platform and is later sent to the bottom level. At the bottom level King Boo appears after the player ground pounds all three purple platforms. The player must defeat him by tossing peppers into his mouth after a slot result gives the player fruit and then must feed him another fruit. Doing this three times gives the player a Shine Sprite. In Super Mario Sunshine however instead of being a boo with a crown and sharper teeth, in Mario Sunshine he is wider fatter and is drooling. This may be a different King Boo.

Mario Kart: Double Dash!!
In Mario Kart: Double Dash!! King Boo is a hidden character who is unlocked after the player finishes the flower cup on Mirror Mode, making him one of the toughest characters to unlock. He is paired with Petey Piranha and like his partner he is a heavy weight however his kart the Boo Pipes is a heavy kart with the speed of a lightweight kart.

Super Mario 64 DS
In Super Mario 64 DS the player must defeat him to save Luigi and unlock him in gameplay. Luigi is an optional character who is required to collect all 150 Power Stars. Mistakenly, King Boo was called Big Boo, who was a 2-time boss at his own haunt.

Mario Superstar Baseball
In Mario Superstar Baseball he is a minor playable character in the power category who is on Wario's team in adventure mode and is a starter character. King Boo bats and pitches right-handed.

Mario Kart DS
In Mario Kart DS he is a boss in mission mode.

Mario Kart Wii
In Mario Kart Wii he is a heavyweight hidden character who can be unlocked after the player finishes the Star Cup on 50cc or if the player plays a total of 750 races.

Mario Party 8
King Boo is the host of his own board entitled King Boo's Haunted Hideaway in Mario Party 8. He'll force the players to traverse through his rearranging mansion and find him at one of three altars (the other two being traps). If a player does manage to find him, the player can buy a Star for 10 coins. He would then send all the players out and rearrange the mansion.

The player could also buy King Boo's sounds and a figurine titled "King Boo's Revenge".

Mario Super Sluggers
He appears as a playable character. He spectated the game at Wario City, turning invisible to not be seen by Bowser Jr. In story mode, King Boo will refuse to join your team unless a Boo is on it. He also gives the hints which are "error item" and "in a box."