King Boom Boo is a collectible card that can be contained by winning the Tails Cup in Single Player. After four hits, King Boom Boo disperses into air. If the player moves too fast when running from him, King Boom Boo will turn around and chase them from the other side. He can be damaged up to three times in one hourglass flip. Knuckles must chase his shadow across the room and dig it up, then run after him and punch him. King Boom Boo then retreats into the ground.
Occasionally, the ghost stops to spew a huge blue wave of flames, and during that time Knuckles must stun King Boom Boo by moving behind him and punching a Boo holding an hourglass, activating the hourglass which opens panels in the ceiling, making light fill the room. In the boss battle, Knuckles runs around a circular arena while followed by King Boom Boo who throws blue fireballs at him (and may also attempt to bite him at close range).
Knuckles encounters King Boom Boo while searching for keys to a door that Sonic, Tails, and Amy were trying to get through.
