Big Boo (Paper Mario series)

Atomic Boo is a Big Boo made up of exactly two hundred different Boos. The Atomic Boo is an optional mini-boss in Paper Mario: The Thousand-Year Door. To fight this boss, Mario must go to the Creepy Steeple after freeing the Boos in Chapter 4 and agreeing to be nice to them, after which all the Boos will come out and swarm him. If Mario knocks the Boos away twice with the Super Hammer by using the Spin Attack, the Boos will combine together to make the Atomic Boo. Atomic Boo attacks by flinging Boos at Mario, charging up a powerful glare attack, hiding his face and becoming invisible like regular Boos, floating over and falling onto both Mario and his partner, and inflicting Mario with status ailments such as confusion and paralysis. Once Atomic Boo is defeated, he will relinquish his Lucky Start badge to Mario and the Boos will stop their swarming and appear as normal enemies.

Atomic Boos were revealed to be a species (at least in the dimension including Flipside) in Super Paper Mario, where a considerably weaker Atomic Boo appears in Merlee's Mansion. This Atomic Boo will attempt to attack the player by charging at them while the are facing the direction opposite of them and will turn intangible and shy away if the player faces it. Also in Super Paper Mario, Atomic Boos will occasionally appear in the minigame Mansion Patrol; though slower than regular Boos, Atomic Boos take several hits to defeat instead a single one. Finally, Tippi states that the Super Paper Mario Atomic Boos are only rumored to be made up of many smaller Boos.

Stats

 * HP: 10
 * Attack: 1
 * Defense: 0
 * Location: Merlee's Mansion
 * Catch Card Number:
 * Tattle: That's an Atomic Boo. That is one enormous Boo...  Max HP is 10.  Attack is 1.  It will follow you until you turn around, then it just disappears...  It has a lot of HP, so you may want to use an item while your back is turned...  Some say this Boo is a huge massive ball of many smaller Boos...

Trivia

 * Oddly, one Boo, known as the Creepy Steeple Boo, sends an e-mail to Mario thanking him for freeing his friends. It is unknown if he was one of the Boos that formed Atomic Boo.
 * A purple variant of Atomic Boo, called Dark Atomic Boo, was found in the game's coding, but cannot be fought. Presumably it would serve as a late-game mini-boss, perhaps in Poshley Sanctum, where the smaller Dark Boos can be found in abundance. It's reasonable to assume that Dark Atomic Boo would have used more powerful versions of Atomic Boo's attacks.
 * Atomic Boo is similar to Boolossus from the game Luigi's Mansion, being that both are made out of many normal Boos. Boolusses may be a type of Atomic Boo.
 * While Boolossus is made from fifteen Boos, Atomic Boo is still smaller than Boolossus, even though he's made out from two-hundred Boos.
 * There are 5 Boos for every Heart Point and 50 Boos For every attack point in the Atomic Boo.
 * The Atomic Boo is composed up of 201 Boos, the 200 in the chest AND the depressed/depressing Boo that wanders around when the player try to enter a door when you first enter Creepy Steeple.