In Super Mario's Mushroom Kingdom, it's undeniable that the biggest bad guy to threaten Princess Peach and her citizens is the Koopa King, Bowser. However, he's not the only villain threatening the safety of the Mushroom Kingdom.

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Ever since his first appearance in Luigi's Mansion for the Nintendo GameCube, King Boo has become a reoccurring boss. Sometimes you play as him, and sometimes he helps you steal coins and stars from your friends. Most of the time, he's here to cause trouble for the Mario brothers and their friends; no matter where the spectral king appears, you can always be sure he's up to no good.

9 Mario Kart 8 Deluxe

Evil Villains Go Go-Karting

Mario Kart 8 Deluxe

Racing Released April 28, 2017 ESRB E Developer(s) Nintendo EAD, Nintendo EPD Publisher(s) Nintendo Platform(s) Switch Genre(s) Racing Powered by Expand Collapse

Several Mario Kart games let you choose King Boo as your champion of choice. He first made his Mario Kart debut as Petey Piranha's partner in Double Dash but has since chosen to drive alone. Some games keep his main series appearance, while other games let you don his more menacing Luigi's Mansion look.

This heavy-tier racer may be choosing not to cause Luigi and his friends too much trouble for now, but there's no telling when the king of the Boos will choose villainy over go-karting next.

8 Mario Party Superstars

He'll Steal For A Price

7

Mario Party Superstars

Party Game Released October 9, 2021 ESRB e Developer(s) NDcube Publisher(s) Nintendo Platform(s) Switch Genre(s) Party Game Powered by Expand Collapse

When Horror Land was originally released in Mario Party 2, the tombstone in the top right corner of the map belonged to Big Boo. When Mario Party Superstars chose to reuse this board, Big Boo was replaced by King Boo instead.

In this game, King Boo is on your side - for a price. If you reach him with the help of a Skeleton Key, King Boo will offer to steal coins or stars for triple the cost of a normal Boo. This is because the ghostly king takes either coins or stars from all your opponents, instead of just one of your choice. He can be integral to turning the tide in a game if you have enough coins to pay for his services.

6 Super Mario Bros. Wonder

Escape His Operatic Chase

Super Mario Bros. Wonder

Platformer 4.0/5 Released October 20, 2023 ESRB E For Everyone // Mild Fantasy Violence Developer(s) Nintendo EPD Publisher(s) Nintendo Platform(s) Switch Genre(s) Platformer Powered by Expand Collapse

King Boo makes a reappearance in Super Mario Bros. Wonder in two stages - Light-Switch Mansion and The Final Battle! Bowser's Rage Stage. In these stages, the spectral king chases your hero of choice while singing in an operatic baritone. If he loses his crown, he shrinks to the size of a normal Boo.

Just like typical Boos, King Boo hates to be looked at. If you choose to stop running and face him instead, he'll cover his face and his singing voice will grow distorted. Who knew such a menacing foe could be shy?

5 Super Mario Sunshine

Try Your Luck Against The King

Super Mario Sunshine

Platformer Released August 26, 2002 ESRB E For Everyone due to Comic Mischief Developer(s) Nintendo EAD Publisher(s) Nintendo Platform(s) GameCube Genre(s) Platformer Powered by Expand Collapse

Technically, the King Boo from Super Mario Sunshine isn't King Boo at all. He's a Big Boo created with the use of Bowser Jr.'s magic paintbrush created by E. Gadd. However, many still consider Sunshine one of the king's many appearances.

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This Boo appears in Sirena Beach's fifth level, leading the Boos who were terrorizing Hotel Delfino. If you manage to access him through the basement casino, a boss battle begins where you have to throw a spicy pepper into his mouth, allowing you to hurt the ghost. Once defeated, he explodes into paint-like goop, rewarding you with a Shine Sprite for your victory.

4 Mario & Luigi: Paper Jam

Tricks And Illusions Are His Specialties

Mario & Luigi: Paper Jam

RPG Released January 22, 2016 ESRB e Developer(s) AlphaDream Publisher(s) Nintendo Platform(s) Nintendo 3DS Genre(s) RPG Powered by Expand Collapse

King Boo is back to no good in the Mario & Luigi and Paper Mario crossover, Mario & Luigi: Paper Jam. When the trio split up in Gloomy Woods, King Boo kidnaps both Mario and Paper Mario, leaving Luigi on his own to find the two. Luigi finds Mario and the two search for Paper Mario. J

Just when they think they've found him, King Boo reveals that it was a disguise to get the better of the two brothers. During the battle, King Boo summons a Paper Boo, holding the real Paper Mario, who the brothers can finally rescue. With the help of Paper Mario, the brothers are able to defeat King Boo once again.

3 Luigi's Mansion

The King's Debut

Luigi's Mansion

Adventure Released November 18, 2001 ESRB E For Everyone due to Mild Cartoon Violence Developer(s) Grezzo Publisher(s) Nintendo Platform(s) Nintendo GameCube, 3DS Genre(s) Adventure Powered by Expand Collapse

Luigi's Mansion was the first true appearance of King Boo, where he tricked Luigi into thinking he won a mansion in a sweepstakes the brother in green never actually entered. Thinking things were suspicious, which he had every right to, Mario goes to the mansion first, only to discover it's full of ghosts. King Boo captures the older Mario brother and seals him in a painting.

King Boo does his best to capture Luigi as well, but the newly ghost-busting brother turns the tide in battle, even when King Boo dons a Bowser suit to attack. In the end, Luigi emerges victorious and seals King Boo in a painting once again.

2 Luigi's Mansion: Dark Moon

Back For Revenge

Luigi's Mansion: Dark Moon

Action Adventure Released March 24, 2013 ESRB E For Everyone // Crude Humor, Mild Cartoon Violence Developer(s) Next Level Games Publisher(s) Nintendo Platform(s) 3DS Genre(s) Action, Adventure Powered by Expand Collapse

King Boo reappears in Luigi's Mansion: Dark Moon, eager for revenge. Having escaped from his painting, King Boo shatters the Dark Moon with a magic bolt from his crown, turning the ghosts of Evershade Valley into chaotic, hostile beings who serve only him.

By the end of the game, King Boo has once again trapped Mario in a painting. He plans to do the same to Luigi, E. Gadd, and the rest of their friends but never gets his chance. Despite his efforts, Luigi collects all six pieces of the Dark Moon and engages King Boo in a final battle, finally sucking the ghostly king into the Poltergust 5000. Luigi then restores the Dark Moon, returning the ghosts of Evershade Valley to their original friendly but mischievous state.

1 Luigi's Mansion 3

His Thirst For Revenge Grows

Luigi's Mansion 3

Adventure 5.0/5 Released October 31, 2019 ESRB E For Everyone due to Comic Mischief, Mild Cartoon Violence Developer(s) Next Level Games Publisher(s) Nintendo Platform(s) Nintendo Switch Genre(s) Adventure Powered by Expand Collapse

King Boo is at his best and most terrifying in Luigi's Mansion 3, where he uses Hellen Graveley to lure Mario, Luigi, Peach, and several Toads to a huge resort. The resort is a trap, operated and filled with ghosts loyal to Hellen and, by extension, King Boo; he manages to seal Mario, Peach, and the Toads in paintings before going after Luigi, but the cowardly plumber manages to escape.

Slowly, floor by floor, Luigi defeats Hellen Gravely's ghostly subjects, giving him more access to the hotel, until he ultimately faces off against King Boo. The king of the Boos is willing to go so far as to destroy the hotel if it means he'll emerge victorious but, ultimately, the king is sucked up by Luigi's Poltergust and placed in a containment jar, alongside Hellen Gravely. This plan may have failed, but we're eager to see what evil scheme King Boo tries next.

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