King Boo is the leader and king of the Boos, the ruler of the Paranormal Dimension, the archnemesis of Luigi, and the main antagonist of the Luigi's Mansion series. He is sinister, clever, and determined in the Luigi's Mansion series. He is considered the arch-nemesis of Luigi and was seen in the beginning of Luigi's Mansion where he ended up trapping Mario in a painting. His powers include causing objects to appear out of and disappear into thin air, and control over fire, ice, and lightning attacks, making him a terrifying and dangerous foe. King Boo consists to be the main antagonist in most Mario series.
King Boo also appears in Mario Kart: Double Dash!! and Mario Kart Wii as an unlockable racer. In Double Dash!!, King Boo teams up with Petey Piranha. His last spin-off appearance so far shows him in Mario Kart 8, but only in the game's Switch version. His design in these games is somewhat cuter, but still somewhat terrifying. Despite having the same name and role, the King Boo from the main games seems to act differently from his first appearance in the Luigi's Mansion spinoff.
King Boo has had two distinct appearances throughout his video game history. In most Mario games since Mario Kart: Double Dash!!, King Boo resembles a normal white Boo with a golden, five-pointed crown, though he is noticeably larger, sometimes at or exceeding the size of a Big Boo. With this design, the crown has a blue jewel on the front and four red jewels around the sides in every game except Mario Super Sluggers, where the colors are reversed. Like other Boos, King Boo is generally shown with an open, wide grin; however, when looked at, he closes his mouth and bashfully hides his face with his hands. In certain games like Mario Party 9, King Boo's emotions are denoted by an aura surrounding him: when happy, he glows with a blue aura, and when angry, he glows with a red aura. Sometimes he also has steam coming out of him to display his anger. In Dr. Mario World, he has a doctor's mirror on his crown and he carries a medicine box by strap. His gold variant in Mario Kart Tour is based on this design, and has an entirely golden body similar to a Gold Boo, though his teeth and tongue are golden as well. His crown is silver and all five jewels are blue.
King Boo's alternate design was first conceived for his debut appearance in Luigi's Mansion and has reappeared in later Luigi's Mansion games. This original design gave King Boo dark red eyes, a blue tongue, two vampire-like fangs, a greenish complexion, and a ruby in a gold, round-edged crown. He is also roughly the same size as other Boos. Starting with Luigi's Mansion: Dark Moon, this design was slightly modified, though it still mostly resembles his original appearance, albeit with a full row of four teeth and large size typical of King Boo's modern design. Other differences include a larger shadow surrounding his eyes, a dark indigo mouth and tongue, and his crown containing a purple jewel and pointed edges. His artwork depicts him with purple eyes instead of red, its color in-game, and without his crown's pointed edges. He has also lost his original green tint, now ranging from purplish to pure white. In Luigi's Mansion 3, King Boo shows more expression, scowling at Luigi when first being found by him and appearing visibly distressed when captured in the game's credits. He also now has purple eyes in-game. His speech icon also uses a green shading reminiscent of his initial appearance, while his portraits show him with a purple crown. In Mario Kart Tour, King Boo's Luigi's Mansion variant uses this design, although his tongue is more purple than indigo. Although King Boo is a lot larger than regular Boos, he is not the largest of the Boos. However, even gigantic Boos like Boolossus follow his leadership despite their superior size. This is likely because he is the most intelligent and the most powerful of the Boos. King Boo seems to have a passion for gambling, as the entrance to each wing in Luigi's Mansion was modeled after a playing card suit (spade, club, heart, and diamond), he is fought atop a slot machine in a casino in Super Mario Sunshine, and (though this is non-canon), his Rival match in Mario & Sonic at the London 2012 Olympics Games is at Bingo Highway, a casino-themed stage from Sonic Heroes. King Boo also has an extreme dislike for the Mario Bros., due to their constant intervention in the plans of the Boo leader and others of his kind, especially towards Luigi. He shows a bit of a snarky side in Dark Moon when he confronts Luigi with a speaking line "Remember when you trapped me for all eternity in a painting? Good times.". Lastly, King Boo has a distinct cackle, which is significantly lower in pitch than other Boos.
King Boo hates spicy things, as throwing a jalapeno pepper in his mouth will set his tongue on fire and make him vulnerable.
King Boo is shown to harbor a deep hatred for the Mario Bros. He claims this is due to the trouble the duo has caused him in the past, presumably referring to all the Boos the Mario Bros. had defeated, as King Boo had not been in any games prior to Luigi's Mansion. His hatred grows towards them in later games, especially Luigi after the latter defeats him in Luigi's Mansion and subsequent sequels. This grudge towards Luigi is reflected in his interactions with the plumber, such as when he childishly insults him in the Luigi's Mansion games and insists on racing against him in Mario & Sonic at the Olympic Winter Games, fully aware of how afraid Luigi is of ghosts.
He says that he fears nothing except the Poltergust 3000, although in Super Mario 64 DS he also admits that Wario's face scares him. In the Mario and Sonic series, he has a superiority complex and is quite prideful. In Mario & Sonic at the Olympic Winter Games, he claims that he is unbeatable at the Alpine Skiing event. In Mario & Sonic at the London 2012 Olympic Games, he claims to have beaten Mario before.
King Boo loves to scare and toy with his opponents, rather than defeating them quickly. In Luigi's Mansion, he chooses to use his powers to blow Luigi back to the foyer instead of trying to finish him off while at maximum power, and enjoys watching Mario struggle from within the painting he was trapped in, stating Mario's desperate attempts to break free were "satisfying."
Despite his huge size and immense power, he still covers his face in fear when looked at, much like a normal Boo, showing that he still has a shy nature like his minions; however, also like a normal Boo, he attacks when his foe's back is turned. King Boo has a distinct cackle, which is significantly lower in pitch than other Boos. He also has an echo in his roar.
King Boo usually considers his Boo minions as friends and cares for them. This is shown in Luigi's Mansion where he goes to free Boolossus after he is captured by Professor E. Gadd, and when he threatens to hurt Paper Mario if the Mario Brothers dared to hurt his Paper Boo minion in Mario & Luigi: Paper Jam. He also has good chemistry with the playable Boo in the Mario Baseball series. In Mario Super Sluggers, King Boo says that he finds little Boos cute.
After breaking out of the portrait he was placed in at the end of Luigi's Mansion, he displays a complete disregard for anything that interferes with his revenge against the Mario Bros. and displays several sociopathic traits, including a disregard for others' well being, and at one point nearly causing the world itself to collapse. King Boo is noticeably less comedic and more openly cruel to Luigi, as well as sadistic, clearly relishing the terrified Luigi's pain with his mind games. Additionally, he no longer cares about his Boo minions, as not only does he not show much concern for them in Luigi's Mansion: Dark Moon, but he even indirectly calls them useless in Luigi's Mansion 3. He does not seem to care for ghosts that are not Boos, instead using them in his plans as tools rather than subjects. Even Hellen Gravely, a ghost who adores him, is seen as nothing more than a pawn or, at best, someone to whom he is indifferent. Professor E. Gadd comments on how King Boo had redecorated the Treacherous Mansion to make it scarier. He also goes into fits of rage when his plans do not go the way he wants. In Luigi's Mansion: Dark Moon, King Boo also has a bit of a sarcastic demeanor as well, as when formally revealing himself to Luigi before fighting him, he references his previous defeat at the hands of Luigi as "Good times", despite clearly being angry and vengeful over it. In Luigi's Mansion 3, King Boo impersonates Mario and Luigi's Italian accent saying, "It's-a me, King Boo!" and uses false comfort towards Luigi. Also in said game, he is shown to have a degree of cunning, as it is strongly implied that he deliberately had Hellen Gravely guard only Mario's portrait in anticipation of Luigi defeating her, and that he could then use Princess Peach's portrait as bait to draw out the Mario Brothers in order to recapture all the portraits, with him very nearly succeeding in this endeavor. Despite being freed by her, he shows no affection for Hellen Gravely or her efforts to impress him, openly stating that he wasn't confident that her plan would work when confronting Luigi, refusing to give her the opportunity to make up for her shortcoming and later disregarding her entirely for her failure upon her capture. He eventually becomes fed up with relying on other ghosts to do his dirty work, deeming them all as useless, and instead decides to forego carefully laid out plans and traps in favor of tackling his enemies directly. During the final battle, he focuses himself entirely on removing his opposition to the point where he is willing to trap The Last Resort and everything around it inside a painting simply to get rid of Luigi. He further shows how much he hates him by attacking him right away despite Mario and Peach being there. Overall, this version of King Boo is a purely evil spirit who disregarded any care he had concerning his subjects. He is the evilest villain in the Mario series by far.
Powers and abilities
- 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.
- ground pound: king boo hits the ground causing shock waves often sending Luigi flying.
Although he commands a large band of Boos, not all Boos call King Boo their leader, with some Boos working directly for Bowser, and many others living peacefully with the other denizens of the Mushroom Kingdom, either independently or as part of a small band of Boos led by Lady Bow. Notably, those Boos that do claim allegiance to King Boo provide him with further power. King Boo has also been affiliated with other ghost enemies, like Peepas.
King Boo initially considered Mario as his main adversary, however after his defeat at Luigi's hands during Luigi's Mansion, Luigi has become King Boo's arch-nemesis. Luigi and King Boo's relationship is often drawn in parallels with Mario and Bowser's, and to lesser extents, Yoshi and Kamek's, and Donkey Kong and King K. Rool's. King Boo also hates Professor E. Gadd for his ghost-capturing hobby, even stating that the only thing that scared him was E. Gadd's invention, the Poltergust 3000. In Luigi's Mansion: Dark Moon, King Boo reveals a desire to get revenge on E. Gadd as well as Luigi, by trapping the scientist within a portrait of his own, something he would later succeed in doing in Luigi's Mansion 3. In Mario Superstar Baseball, King Boo has negative chemistry with Luigi and Baby Luigi; in Mario Super Sluggers, he is shown to also have bad chemistry with Mario, the princesses, their infant counterparts, and Yoshi. In Luigi's Mansion 3, Princess Peach is among King Boo's victims to be turned into portraits. Once Luigi rescues all the Toads, King Boo takes possession of Peach's picture, knowing that Luigi will come for her once he saves Mario from Hellen Gravely.
King Boo has been shown to work with Bowser on numerous occasions, including Super Mario 64 DS, Mario Party 9, and Super Princess Peach. He also used a Bowser decoy and the two share a portrait after King Boo's defeat in Luigi's Mansion. Despite their apparent alliance, the two share neutral chemistry in Mario Superstar Baseball and Mario Super Sluggers, with King Boo appearing on Wario's team, rather than Bowser's. King Boo has also been paired up with Petey Piranha as in Mario Kart: Double Dash!!, with the two sharing chemistry in the Mario Baseball games, although their relationship has never been fully explored. King Boo has good chemistry with Wiggler and King K. Rool in Mario Super Sluggers, though his relationships with both characters, like Petey Piranha, remain unexplored. Luigi's Mansion 3 shows King Boo having a dedicated fan in Hellen Gravely, who releases him to impress and aid him in his plot for revenge against Luigi. Despite her infatuation for him, King Boo sees her as just a pawn in his plan for vengeance and is, at best, indifferent to her. When Luigi frees nearly all his friends, leaving only Mario and Peach to saved, King Boo retains low faith in her capabilities and leaves her to defeat Luigi if she succeeds or be captured if she fails as part of his contingency plan; he eventually deems her useless for being unable to subdue Luigi and keep his friends imprisoned.
Super Mario series
King Boo returns 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 his 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 into the mouth as King Boo tries to recover. 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, but still retains his crown.
This may be because Bowser Jr. painted him, and he doesn't like King Boo stealing Bowser's thunder as big bad boss o' Mario, which is further backed up by the fact that he turns invisible in Super Mario Sluggers to hide from Bowser Jr.
Super Mario 64 DS
In Super Mario 64 DS, Mario must defeat King Boo to save Luigi, and unlock him in gameplay. Luigi is an optional character who is required to collect all 150 Power Stars. Mistakenly, in his Super Mario 64 DS appearance, King Boo was called Big Boo, even though the actual Big Boo was a 2-time boss at his own haunt. Regardless, King Boo aids Bowser in his conquest of Peach's Castle by capturing Luigi and imprisoning him in Big Boo's Haunt. Specifically, Luigi is imprisoned behind a painting of himself inside the haunted mansion. Mario heads to the Big Boo Battle level to save Luigi. Upon entering the level, he is greeted by King Boo, and from there he must listen for King Boo's cackle and enter the door where it is loudest. Eventually Mario reaches the end and fights King Boo to free Luigi. To defeat King Boo, Mario has to follow King Boo's movements in the arena's mirror and stomp him when he comes close enough. Ultimately, Mario saves his brother from King Boo and together (with Yoshi and Wario once he is saved) they defeat Bowser and save Princess Peach. This is corrected when he and the other Super Mario 64 (DS) bosses return in Mario Kart DS. King Boo does not appear in the Nintendo 64 console version of the game due to the fact that he didn't exist when the original game came out.
King Boo makes a small cameo in New Super Luigi U and New Super Mario Bros. U Deluxe in the Secret Exit of Vanishing Ghost House, where his art from Luigi's Mansion: Dark Moon can be seen in the form of a sign hanging from the side of the building.
Mario Sport series
Mario Superstar Baseball
King Boo is a playable character in Mario Superstar Baseball, and a member of Wario's baseball team, the Wario Greats. He is a default character, meaning he does not need to be unlocked. He is a power hitter, using his white, crowned, Boo-like baseball bat to hit long outfield drives and even homeruns. King Boo has good chemistry with Boo and Petey Piranha, and he has bad chemistry with Luigi and Baby Luigi. However, like Boo, his hits are usually very curved, and this causes them to be fouls most of the time.
Mario Super Sluggers
King Boo appears as a playable character and is one of the few characters on Wario's team in both games, along with Boo and Waluigi. He is once again a power hitter, and he also excels in pitching, with both stats being his highest, though his running and fielding are still rather poor. 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." he has good chemistry with Petey Piranha King K. Rool Wiggler and Boo but he has bad chemistry with Mario, Luigi, Yoshi, Baby Mario, Baby Luigi, Baby Peach, and Baby Daisy.
His baseball bat no longer has a physical crown on it. In this game, it is represented as a crown picture above the "Boo mouth" picture. As well, in this game only, the colors of the jewels on his crown are reversed.
Mario Kart series
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 alongside his partner Petey Piranha, making him one of the toughest characters to unlock. King Boo is paired with Petey Piranha and, like his partner, is a heavyweight. However, his kart (the Boo Pipes) is a heavy kart with the speed of a lightweight kart. Just like the Boss Pakkun himself, he can also use any Special Item. King Boo appears to slightly shrink when he becomes the driver. On the second "Thanks for Playing!" screen (after beating the Special Cup with a Gold Trophy while all other cups already have a Gold Trophy), King Boo appears in the background chasing Wario and Waluigi.
Mario Kart DS
In Mario Kart DS, King Boo is a boss in the fourth level mission mode, the playable character is Peach. His stage is a lava arena. 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.
King Boo does not appear in the original Wii U version of Mario Kart 8.
Mario Kart Tour
King Boo returns in this new installment of the Mario Kart franchise. He appears two times: 1. As his normal self 2. As his Luigi's Mansion counterpart (as a highlight). The first King Boos special item is the Lucky Seven, the second King Boos special item the Bob-Omb Cannon. Both of them are relatively hard to unlock, considering the 1. King Boo is a rare driver and the 2. King Boo a high-end (spotlight) driver.
Mario Party series
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. King Boo does not rearrange his mansion upon meeting him in the Star Battle Arena, making his room easier to find the second time.
The player could also buy King Boo's sounds and a figurine titled "King Boo's Revenge."
Mario Party 9
King Boo appears as the stage boss of the board Boo's Horror Castle in Mario Party 9. He is fought in the minigame, King Boo's Puzzle Attack, where the competitors line up power-ups in lines of three or more in his grid to deal damage to him. Once his health reaches halfway, King Boo throws Boos onto the field which can stun the player's cursors, making them unable to move until they shake the Boo off. What is unique about his boss battle is that if a player gets the Final Attack, they get ten points instead of the usual three, likely because the players can easily accumulate points up to fifty. In the final fight against Bowser, King Boo can also appear to hinder the players' progress. If Bowser throws the die with all the stage bosses' faces on it and King Boo's face appears on top, King Boo materializes above the stage. Then, he summons five Boos that move in a counterclockwise direction while moving outwards. When the Boos reach the boundaries of the stage, King Boo summons another five Boos, except this time they move clockwise. The Boos cost points on contact. After his attack, King Boo disappears from the battle unless his face appears on the top of the die that Bowser uses to summon him and other bosses again.
Like most other characters in the game, King Boo has a constellation that can be returned to the sky; it is called the Ghost Major. It is located in the farthest left portion of the sky, near King Bob-omb's constellation and right next to Boo's constellation. Like all constellations, it can be bought for fifty Minigame Points. Also, in the Museum's Sound Test, there are two voice sounds with the name "King Boo's Entrance"; one is of King Boo and the other is actually of Boo.
Mario Party 10
King Boo reappears in the next title, Mario Party 10. He returns as a boss in the minigame King Boo's Tricky Tiles, which takes place in a swampland. At the very start of his game, King Boo appears flitting around the trees that surround the swamp, only to surprise the players. In order to defeat him, the player must remember which platforms are false, and then run around until they can jump on a light switch (one is worth 3 points, and another worth 1 point). Like other bosses, King Boo gets angered after the players deplete his health halfway. The technique that King Boo uses is that he swaps Boos with platforms, and he blocks the camera, so the player can't see the platforms very well and remember which ones are false. He can also be seen on the Luigi Board, which appears in the game's amiibo Party mode.
Mario Party Star Rush
King Boo returns as a boss in Mario Party: Star Rush with his minigame being King Boo's Light Smite. In order to defeat him, players have to use Light Boxes which they need to carry over rotating platforms while evading Peepas. When King Boo loses half his health bar, the rotating platforms start moving faster and more Peepas appear, making it more difficult to reach the other side where King Boo makes his lair.
Mairo Party Superstars
King Boo appears in Mario Party Superstars on Horror Land, replacing the Big Boo found on the original board. He summons Boo lackeys to steal coins (for free) or Stars (for 150 coins) from all opponents who have any. As with the Big Boo in the original, he can only be encountered at night, and only through a path that requires a Skeleton Key.
Luigi's Mansion series
Prior to the events of Luigi's Mansion, Professor E. Gadd captured Boolossus. Using a device called a Ghost Portrificationizer, E. Gadd trapped Boolossus in a portrait and hung it in his Gallery inside his lab in Boo Woods. This angered King Boo, so he devised a plan to rescue Boolossus.
King Boo and his forces attacked the laboratory. The Boos reversed the settings of the Portificationizer and released Boolossus. King Boo then ordered that all the ghosts that E. Gadd had captured should be released as well. After releasing all the portrait ghosts, King Boo created a huge mansion and placed it next to the professor's lab. King Boo, his Boo minions, and the recently freed portrait ghosts decided to inhabit the mansion. With a huge mansion and an army of ghosts, King Boo decided to exact revenge upon Mario and Luigi for all the Boos they attacked during their adventures by capturing them.
Hoping to capture Luigi, King Boo sends him a letter. The message states that Luigi has won a mansion in a contest and provides the location of the prize. Luigi asks his brother Mario to investigate the mansion and says that he is arriving shortly thereafter. Mario travels to the mansion on his brother's behalf, but, right after he enters, is instantly overwhelmed by King Boo's forces and captured. King Boo then imprisons him in a portrait, similar to how Boolossus was imprisoned. Mario is placed in the Secret Altar in the basement of the mansion. With Mario captured, King Boo is ready to capture Luigi.
While waiting for Luigi, King Boo and his Boo minions wait behind a secret door in the floor of the Storage Room. When Luigi enters the room and reveals the secret door, the Boos spring out from the floor. However, the Boos (including King Boo) stop their surprise attack when they notice the Poltergust 3000 on Luigi's back. Luigi had been given the Poltergust 3000 by E. Gadd so he could recapture the Portrait Ghosts and save his brother. The Poltergust 3000 is one of the few things King Boo fears, and he and the other Boos scatter and hide in the mansion. King Boo travels to the Secret Altar in the mansion's basement.
The special key that Vincent Van Gore holds unlocks the path to the Secret Altar. However, he is locked in The Artist's Studio on the third floor of the mansion. After capturing him and retrieving the key, Luigi discovers that he still cannot enter the Secret Altar. If Luigi attempts to enter the Secret Altar without catching a certain number of Boos, King Boo blows Luigi to the Foyer, the entrance of the mansion. Since King Boo's power is related to the number of Boos in the mansion, Luigi can weaken him by capturing the Boos hidden in various rooms. After Luigi captures at least forty of the mansion's fifty Boos, King Boo loses his ability to blow Luigi from the Secret Altar. Once King Boo is weakened, Luigi enters King Boo's Secret Altar.
Upon entering the Altar, Luigi notices King Boo staring at Mario in the painting while insulting the brothers' intelligence for having fallen for his scheme. King Boo then turns around to face Luigi and states his desire to add a Luigi painting to the collection. After this, King Boo flies into the Mario painting hanging on the wall. The picture of Mario transforms into Bowser, then the new Bowser painting inhales Luigi into the canvas, transporting Luigi into an arena that resembles the mansion's roof. Luigi then confronts Bowser. In reality, this is a suit of Bowser that King Boo controls from the inside and uses as a shield for his own body.
King Boo uses this Bowser suit to attack Luigi, shooting flames at him causing ten HP of damage, and even attempting to inhale him into its mouth, deducting fifteen HP upon spitting him out. The suit also has the ability to create three large spiked bombs and toss them at Luigi, which when exploding, take away ten HP. Luigi can use his Poltergust 3000 to grab one of the spiked explosives and release it into the Bowser suit's mouth. This attack blasts the head off of the Bowser suit, causing King Boo to exit the shield and expose himself to the Poltergust 3000. Luigi begins to deplete the ghost's five hundred hit points. Meanwhile, the suit's head hovers around the arena, shooting icy blasts at Luigi, which freezes him briefly. King Boo, after a while, flies back into the dormant Bowser body and the head reattaches itself, resuming the fight. Luigi repeats this process, slowly weakening King Boo, but after King Boo's life falls below two hundred HP, the head of the suit reattaches backwards whenever he returns to the Bowser body, causing the Bowser suit to run around aimlessly. The suit soon corrects its head and resumes the fight. Eventually, Luigi manages to completely drain King Boo's HP and capture him inside the Poltergust 3000.
After the battle, Luigi receives King Boo's crown, worth 5000G, and adds it to his treasure collection. Upon returning to the mansion, Luigi quickly travels to Professor E. Gadd's lab. In the lab, Luigi connects the Poltergust to the professor's Portrificationizer, dumping its contents into the machine. Both King Boo and the fake Bowser appear on the Portificationizer portrait. With King Boo captured, Professor E. Gadd hangs his new portrait in an empty room in his gallery.
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 (much to Elvin's own horror ("What in tarnation!?")), 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 as King Boo fights with all his might and may, but it ends with King Boo being once again trapped in the Poltergust 5000 and Luigi stealing the ruby atop his crown and using it to reveal the painting that Mario was trapped in.
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 of 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." This implies that there may 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.
King Boo reappears in Luigi's Mansion 3 with the same design as in Luigi's Mansion: Dark Moon. King Boo, having been released by Hellen Gravely, the owner of the hotel and a big fan of his, in order to impress him. Seeking revenge on Luigi for his previous defeats, he traps Professor E. Gadd, Mario, Princess Peach, and the three Toads in portraits before going after Luigi, who manages to escape his capture by going down a laundry chute.
He later ends up entrusting Hellen Gravely with Mario's portrait, although it's implied that he intended for Luigi to win both due to Gravely's failures by that time and so he could capture both alongside Peach by using the latter as bait, also recapturing the Toads and Professor E. Gadd just after Mario was freed. However, he ultimately fails to capture Luigi atop the hotel due to Polterpup shoving him out of the way as King Boo lowers his Portrait Frame, which results in a fight.
To defeat King Boo, Luigi must throw a bomb from a spiked ball King Boo throws into his mouth, then pull on his tongue with Gooigi's help and slam him repeatedly. Upon doing so, King Boo will then generate a clone that attacks alongside him. After this is done twice, King Boo will enlarge the painting, and Luigi will then have four minutes to attack King Boo one last time. The battle ends with King Boo being recaptured by Luigi and placed in a containment jar alongside Gravely, much to his chagrin. As the purple gem in his crown was taken by Luigi after the final battle, it is missing from his crown.
If the player gets a game over at any point during this game, King Boo will be shown trapping Luigi in a portrait alongside the rest of his friends.
King Boo appears in Shriek Mansion as the boss. 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 a low life, he cries with many tears to extinguish the lanterns. This makes it recommended to light the top lanterns first, as King Boo can only fire his tears (which Peach can touch without getting damaged, though she will still take damage from contact with his body) downwards. However, said tears dissipate after a certain range, so it is possible to light the bottom lanterns first, then the top. Plus, King Boo moves slowly during his fight.
After finishing him off, King Boo enlarges and disappears as his crown explodes. This rewards her the kidnapped Toad.
King Boo appears as a boss in Mario & Luigi: Paper Jam, making his official Mario & Luigi series debut. King Boo has a Papercraft version of himself controlled by Morton and Lemmy, which is fought in Bowser's Castle. The Mario Bros. use Papercraft Yoshi to fight it.
The real King Boo is encountered and fought in Gloomy Woods after the trio separate, leading to him kidnapping Mario and Paper Mario; leaving Luigi alone to find them, like in the Luigi's Mansion series. After finding Mario, Luigi begins to look for Paper Mario alongside him. They eventually find King Boo instead, disguised as Paper Mario. When they group together, King Boo reverts back to his normal form and laughs at the Bros. for a second, before re-transforming; Mario and Luigi then turn around, and are unaware of King Boo's presence. When they turn around again, King Boo reveals himself again, but is caught by the duo before he can transform back. In an attempt to fool them, the Boo King immediately reverts back to Paper Mario, and tries to convince the Bros. that he is the real Paper Mario, but fails. King Boo then loses control of his transformation powers, as he quickly transforms into Paper Peach and then Paper Bowser, before finally gaining control and giving up; reverting back to his true form, causing the battle to commence.
King Boo attacks by spitting blue fireballs at either Mario or Luigi before inhaling them; making them need to avoid the fireballs twice, and splitting into five copies before floating slowly towards the trio, turning invisible as he gets near; which the trio must counter using their hammers around 2 seconds after a copy turns invisible. King Boo takes the same damage that his copies do, but hitting him will not end the attack immediately unless King Boo was the last one. During the battle, King Boo calls a Paper Boo holding the real Paper Mario onto the battlefield; threatening to harm Paper Mario if the bros attack either himself or the Paper Boo. In order to save Paper Mario, Mario and Luigi must defeat the minion holding onto Paper Mario, causing it to drop him. If King Boo is attacked while the Paper Boo is on the battlefield, he deals damage to Paper Mario. After a few turns, another Paper Boo can grab Paper Mario again, taking him out of the battle (which gets rid of Paper Mario's copies) temporarily. This cannot be avoided. Finally, King Boo also has a chase attack where he grows bigger before attempting to shoot a giant blue fireball from his mouth at the trio; which Mario and Luigi have to counter by throwing Paper Mario's boomerang form into King Boo's mouth while it is open. Once defeated, Paper Mario is reunited with the duo and the group continues to Mount Brrr.
Due to his crown, King Boo is immune to the brothers' Jump attack (but he can be hit by Hammer attacks as compensation, in case the Bros. run out of Special Points and syrup, unlike Paper Boos) and certain Bros. Attacks, such as the Rocket Blast and Mega Thwonk's jumping attacks (only in the arcade), possibly due to them striking his forehead. Attacking King Boo using attacks from above results in the Bro. taking 1 damage as if they were jumping on a spiked enemy. The Dropchopper, however, can circumvent this as it can be aimed towards King Boo's forehead instead of his crown and can then damage him.
The splitting attack used by King Boo is a reference to (if not a direct copy of) the Dark Star's splitting attack in Mario & Luigi: Bowser's Inside Story, except King Boo takes damage if countered unlike the Dark Star's version due to it being invincible. As well, if the Mario Bros. continue to attack King Boo without freeing Paper Mario, his slapping Paper Mario may be an allusion to Lady Bow and her slap attacks. Also, King Boo's voice clips from Mario Kart Wii are reused. Prior to fighting King Boo, a Papercraft King Boo is fought in Bowser's Castle piloted by Morton Koopa Jr. and Lemmy Koopa.
- 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.
- 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.
- King Boo usually uses his tongue to mark which direction he is going. This can be useful if you're lost.
- 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 on his tail, or turning his "head" to look behind him will result in turning his whole body.
- In Luigi’s Mansion 3, during the final battle, the clones that King Boo summons in the final battle reference his original design from Luigi's Mansion, as they only have two teeth, lacking the middle two fangs King Boo is depicted with now.
- The crown from Dark Moon may be a variation off of his original crown, mixed with the Dark Moon shard preventing it from being a full moon.
- This is further backed up by his eyes being shaded purple and the area around them being shadowed.
- His Luigi's Mansion counterpart along with Dimentio, Shadow Queen, and Princess Shroob are the only four Mario villains to be considered Pure Evil.
- He is the only boss in Luigi's Mansion 3 to be a time limit boss.
- Although he commands a large band of Boos, not all Boos call King Boo their leader, with some Boos working directly for Bowser, and many others living peacefully with the other denizens of the Mushroom Kingdom, either independently or as part of a small band of Boos led by Lady Bow.
- The purple moon-like glowing things King Boo gets when he's stunned from throwing one of his own bombs back at him and having it land in his mouth in Luigi's Mansion 3 may be a reference to Luigi's Mansion: Dark Moon.
- It is possible that King Boo's malicious and destructive behavior following his first defeat was a result of his new magical crown corrupting him and driving him to madness.