Luigi's MansionIn Luigi's Mansion, King Boo makes a haunted mansion and sends a letter to the Mario Bros, stating that Luigi won a grand mansion in a contest(that Luigi never attended). About the same time, he releases all the portrait ghosts Professor E.Gadd has caught before and later catches Mario(who went to the mansion himself 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 the Professor who gives him the Poltergust 3000 and tells Luigi how the Boos freed all of his Portrait Ghosts. Luigi then sets off to save Mario, but later on, he ends up in a storage room and frees all fifty Boos, as well as King Boo himself; Luigi then 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, King Boo pilots a giant Bowser mecha (intricately made to look just like Bowser, although a false Bowser) to help him battle Luigi. The player must defeat him by tossing a spike ball at the Bowser robot'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 with the fake Bowser suit. He has the exact same role in the game's remake.
Super Mario SunshineKing Boo returns again in Super Mario Sunshine, in which he is the boss of episode five of Sirena Beach. To reach him, Mario must head to the casino of Hotel Delfino and Ground Pound a purple platform, which is later sent to the bottom level. At the bottom level King Boo appears after he does a creepy laugh and the wheel will start to rotate; ground pounding the purple platforms will stop one section of the wheel. Mario must defeat him by tossing peppers into his mouth (after a slot result gives Mario fruit) and then tossing another fruit at the Boo. Doing this three times earns Mario a Shine Sprite. In Super Mario Sunshine, however, instead of being a Boo with a crown and sharper teeth, he is wider, fatter, and drooling.
Mario Kart: Double Dash!!
In Mario Kart: Double Dash!!, King Boo is a hidden character who is unlocked after the player finishes the Star 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 heavyweight; however, his kart (the Boo Pipes) is a heavy kart with the speed of a lightweight kart. He can also use any Special Item.
Super Mario 64 DS
In Super Mario 64 DS, Mario must defeat him to save Luigi, his brother 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
Super Princess Peach
King Boo appears in Shriek Mansion. However, the lanterns go out. As a result, the Toad will fade with the bubble and the three Boos. King Boo suddenly becomes less transparent and the crown lands on his head.
King Boo has few starting attacks: floating towards Peach and send blue fireballs. To attack him, Peach should use the Rage vibe to lighten up the four lanterns. As a result, King Boo will disappear and his crown falls to the ground. He reverses the lanterns off and continues the battle.
When he has low life, he cries with many tears to extinguish the lanterns.
After finishing him off, he enlarges, disappears and his crown explodes. This rewards her the kidnapped Toad.
Mario Kart DS
In Mario Kart DS, he is a boss in the fourth level mission mode, the playab character is Peach. Here, the player has to collect fifty coins from him. When he takes them, the player must try to get them when he is teleporting and continue collecting coins.
Mario Kart Wii
Despite being an excellent handler, King Boo is a mid-tier character for his poor raising stats. King Boo is a good choice for courses with tight turns, such as Rainbow Road. Despite his mid-tier placing, King Boo has great rivalries with other characters and has excellent racing skills, making him a character with high-tier or possibly top-tier character categories since his handling stat raises any kart or bike, including the Spear.
Mario Kart 8 Deluxe
King Boo returns to Mario Kart 8 Deluxe as a new playable character along with Bowser Jr., Dry Bones, Inkling Girl, Inkling Boy, and Gold Mario. He is controlled by the 200cc staff ghost, Nin★Rui (from Portugal) on a Wild Wiggler with Sponge tires and Flower Glider with the time of 1:38.244 for Twisted Mansion.
Mario Kart Trivia
- Interestingly, King Boo is one of the Heavyweight characters, despite being a floating, weightless ghost. This may be due to the weight of his crown or his large size.
- He usually uses his tongue to mark which direction he is going. This can be useful if you're lost.
- Despite being a "weightless" heavyweight, King Boo is actually heavier than Wario and Waluigi, the same weight as Rosalina and is a tad bit heavier than Dry Bowser .
- King Boo is the only character in Mario Kart Double Dash!! to not yell or say anything when being shot from the cannon in DK Mountain. (Though in Mario Kart Wii, he does.)
- When the player drives behind him and a blue wave appears, he doesn't turn his head to look behind him like all the other characters. This is probably because he already knows that you're behind him, or turning his "head" to look behind him will result in turning his whole body.
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 ten 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 Party 9
King Boo appears to be the third stage boss in Boo's Horror Castle with his own boss minigame, King Boo's Puzzle Attack. He will send out Boos to attack the players as they shift the powerups to match and attack him. After he turns furious, he'll use two instead of one.
Mario Super SluggersHe 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".
Luigi's Mansion: Dark Moon
King Boo returns as the main antagonist of Luigi's Mansion: Dark Moon. He is seen destroying the Dark Moon in the opening cutscene, causing all the ghosts of Evershade Valley to lose control and run rampant throughout the mansions located there. Though he does not reveal himself to Professor E. Gadd and Luigi at first, numerous Boos are seen throughout the game, and the king himself makes several cameos before his grand appearance, all of which are short, subtle, and with his back turned. In several security camera images seen in the game, Boos are seen carrying a sack with an odd portrait of what appears to be a person. When Luigi gets to the last mansion, the Treacherous Mansion, he shines his light into the dark entrance. When he sees nothing, he turns around and looks for anything that may be behind him. After he turns around, King Boo appears and grins at him menacingly.
Once Luigi rescues the two Toad Curators from the Treacherous Mansion, the final security image reveals that the painting being carried around is in fact Mario, who has been once again imprisoned by King Boo. King Boo, also in the image with his back turned, suddenly turns around and reveals himself to E. Gadd and Luigi, and causes the lab's screen to go fuzzy. Luigi goes into the Mansion's train exhibit to ambush the king, only to be attacked by a Big Boo made of ten smaller Boos that Luigi shoots to the train.
Luigi defeats Big Boo, and then the Tough Possessor to nab the final piece of the Dark Moon. However, before he can return to the lab, Luigi's Pixelation is intercepted by King Boo, and Luigi is sucked into his illusion. There, King Boo taunts Luigi and confesses that he destroyed the Dark Moon and trapped Mario in a painting so he could seek revenge on Luigi(and E. Gadd) and become ruler of the world. An intense battle ensues, and ends with King Boo being once again trapped in the Poltergust 5000 and Luigi stealing the ruby atop his crown.
Oddly enough, King Boo is not seen in the Boo Vault after the game's completion. However, he can be re-fought as many times as the player would like in the level King Boo's Illusion.
Though it is not officially revealed how King Boo escaped his painting, E. Gadd notes that he "shouldn't have sold it at a garage sale", implying that there may be have been some external force helping to free King Boo.
To defeat him, make him slam the floor, making spike balls summoned earlier into the air and make him stay in the spots where the balls will drop. This will stun him before Luigi is able to start vacuuming.
Mario & Luigi: Paper Jam
King Boo is seen at Gloomy Woods during the second visit where he has taken control over the forest. King Boo makes his presence known where Mario, Luigi, and Paper Mario inspect an odd tree. Luigi runs off scared but when he returns seconds later, it is shown King Boo has captured Mario and Paper Mario forcing Luigi to look for them alone. Mario and Luigi eventually reunite and find Paper Mario on the other side. However, it turns out to be King Boo in disguise and then fights them in battle.
- Invisibility: King Boo being king of the boos can turn invisible however being a boo master it can use the most compelling powers of invisibility.
- Boo Call: King Boo can use his crown to call more boos.
- Slot Machine: only seen in Super Mario Sunshine, King Boo can use a slot machine to determine what items Mario can get.
- Portal: King Boo can also create portals to escape to other dimensions.
- One of King Boo's lines from Luigi's Mansion is a reference to Star Wars: Return of the Jedi "I will not give up on my favorite decoration. I like Mario just where he is" He says this if you confront him before the end of the game.