King Boom Boo

"What the...a ghost?"

- Knuckles the Echidna, Sonic Adventure 2

King Boom Boo (キングブーブ) is a boss in Sonic Adventure 2 and its remake Sonic Adventure 2: Battle. He is a colossal ghost and the king of ghosts who leads the Boos and Boom Boos. He is encountered and fought by Knuckles the Echidna after clearing Death Chamber.

Sonic Adventure 2
Knuckles the Echidna encounters King Boom Boo whilst searching for the keys to a door which Sonic the Hedgehog, Miles "Tails" Prower, and Amy Rose are trying to get through. During the boss battle, Knuckles is chased around a circular arena by King Boom Boo, who throws blue fireballs at him and attempts to bite him at close range. Occasionally, the ghost pauses and spews a large blue wave of flames. During this attack, Knuckles must activate an hourglass which opens panels in the ceiling, flooding the room with light and causing King Boom Boo to shrink. His shadow sinks into the floor or the wall, and Knuckles has to dig it up and bring the ghost to the surface. At this point, the player must run after King Boom Boo and punch him before the hourglass runs out, clearing the light from the arena and causing him to grow back to his normal size. He can be damaged up to four times in one hourglass flip. If the player runs too fast, he moves in the opposite direction.

Sonic Rivals 2
King Boom Boo appears as a collectible card in Sonic Rivals 2. It can be unlocked by winning the Tails Cup in Single Player mode. The card unlocks Tails' Captain suit.

Personality
King Boom Boo is hostile and mischievous, laughing merrily when causing harm to Knuckles. However, when the odds turns against him, he will try to run away. He also has a great aversion to sunlight and will try to hide from it. He appears incapable of coherent speech, only giving off babbles, grunts and roars.

Powers and Abilities
As a ghost, King Boom Boo has several supernatural powers. He is capable of levitation, allowing him to float in midair and can move fast enough through the air to keep up with Knuckles' running speed. He also possesses a degree of pyrokinetic abilities which lets him either form blue fireballs in his hands and throw them like projectiles or blow a large torrent of blue flames from his mouth. He can as well transform into a dark shadow of himself which lets him move along floors and walls, though he can removed from a surface by force which will make him revert back to his normal form. He can also seemingly turn himself invisible.

King Boom Boo's strength is tied to the light; when in contact with darkness and shadows, his powers are at their peak, allowing him to become bigger, stronger and seemingly invulnerable. Consequently, he is weakened when coming into contact with sunlight, making him shrink and vulnerable to attacks.

Sonic X
King Boom Boo also made an appearance in the Sonic X anime series and its comic series published by Archie Comics. In this continuity, he and his minions of Boos haunt an ancient castle on earth.

King Boom Boo first appeared in the episode "Sonic's Scream Test", where he and his Boos kidnapped Sonic and the majority of his friends after the talisman keeping them trapped in their world was removed, with the goal of emerging in the living world. However, King Boom Boo was stopped and returned to his world thanks to the united efforts of Sonic and his friends

In Sonic X #14, King Boom Boo returned, having been summoned to an island when the talisman was taken there. There, King Boom Boo began possessing the islanders so he could enter the living world for good, but was convinced by Chris and Cream to return to his eternal sleep.

Trivia

 * King Boom Boo's presence can be seen at the giant pillars in Pumpkin Hill and in Aquatic Mine
 * King Boom Boo was suggested as a new character for issues of the Archie Comics following Sonic the Hedgehog #134, but the plot line in which he was intended to feature appears to have been cut.
 * King Boom Boo is the only boss in Sonic Adventure 2 to have green text appear on-screen before facing him.
 * Although it's never shown, it's arguable that Knuckles was afraid of King Boom Boo, as when he notices him, he says "What the... a ghost?!", but he only says it with a little shock and disbelief. However, in an unused line, Knuckles says "What?! A ghost!" in a more frightened tone, and in the Japanese version, Knuckles says "O-Obake!", meaning "G-Ghost!", and he is clearly scared.
 * King Boom Boo resembles the Boos from Nintendo's Mario series. His name even contains "Boo".
 * When fighting him, the player can see a picture of a Nintendo Boo and a regular Boom Boo on the wall.
 * King Boom Boo actually came before Nintendo's King Boo. King Boo's first appearance was in Luigi's Mansion, which was released the same year as, but several months after, Sonic Adventure 2.
 * King Boom Boo and the other ghosts in Death Chamber look similar to Hyudoro in Sandopolis Zone in Sonic & Knuckles. Also, both of them inhabit pyramids.
 * There is a glitch in the PlayStation Network port, when the windows on the roof of Boom Boo's arena are opened if the player pauses the game. The sky will change from blue to black. If the player resumes the game, the sky will return to its normal color. However, if the player restarts the game from the pause menu, the sky will stay black for the rest of the fight.