King Boo

King Boo is a boss in Super Mario 64 DS, found at the end of the Big Boo Battle level. They take the appearance of a Big Boo with a crown, and their arena is a mirror room similarly to the one seen in the Second Floor of Princess Peach's Castle. Beating them unlocks Luigi as a playable character.

Boss Fight
Before King Boo is fought, the player enters it's arena which takes the appearance of a large mirror room. The player must approach the mirror, where their reflection will turn into Luigi, before King Boo appearing and talking to the player before the fight properly begins.

The King Boo boss fight functions the same as a Big Boo, though they are only visible in the mirror except for their shadow, and can spit blue flames that damage the player. When looked at, they go invisible, similarly to a regular Boo and Big Boo. They also have the ability to switch to the main segment the player is in, and then become invisible in the mirror, and also switch back to the reflection.

They are also damaged the same way as a Boo and Big Boo, by being ground pounded with the player's back turned towards the boss so they don't go invisible and become invincible. They take 3 hits to defeat, and drop the key to unlock Luigi's door when defeated.

Super Mario 64 Manifestation
In some personalized copies of Super Mario 64, King Boo can manifest alongside Big Boo Battle. They most commonly end up being replaced by a Big Boo, though can appear as a separate boss fight following the same patterns seen in the Super Mario 64 DS appearance. Defeating them usually rewards the player with a star, as character keys usually do not appear in personalized copies.

Name Error
In Super Mario 64 DS, despite King Boo being an entirely separate boss from Big Boos, they are referred to as a Big Boo in dialogue, and in the name of Big Boo Battle. This could have potentially been a translation error, though this is unconfirmed.

Appearance Changes
In certain personalized copies of Super Mario 64 DS, an uncommon phenomena may occur, in which King Boo might look like either his appearances in Luigi’s Mansion or Super Mario Sunshine. This generally does not affect the battle, but it’s been said that some copies in which Sunshine King Boo appears, he uses his tongue for an attack. Luigi’s Mansion King Boo has also been said to use spiked balls (Like the ones used in his battle in Luigi’s Mansion) in one of his attacks.