Boo

The Boo (ブー) is an enemy that first appeared in Sonic Adventure 2. They are a breed of ghosts who inhabit haunted areas and are the servants of King Boom Boo.

Appearance
Boos typically have white body round bodies. Normal types of Boos have black, soulless eyes, mouths that have been knitted up, small thin hands, and two small sharp on their bottom which resemble legs.

Attack type Boos are larger and have red and orange maniac eyes with black pupils, sharper hands with three pointy fingers and the two ends on their bottom have merged into one. Their mouths are also opened, revealing sharp black teeth.

Personality
Similar to their king, the Boos are mischievous and malicious, giggling whenever they cause misdeeds. While normal Boos are rather passive, attack type Boos are much more energetic.

Powers and abilities
The Boos have the ability to levitate and move through midair. As ghosts, they can turn themselves invisible and possess a spirit physiology that causes them to evaporate whenever they takes too much damage while tangible.

Sonic Adventure 2
The Boos first appeared in Sonic Adventure 2 and its later iteration Sonic Adventure 2: Battle. The can be found in the following Stages for each character:

In this game, there are two types of Boo: the ones with black eyes (normal types) and those with red and yellow eyes (attack types). Normal Boos are harmless and scurry along the ground, but will also hide in gravestones, pumpkins, and even just in the ground. When approached, these Boos will pop up in the playable character's face to feign an attack. This does not inflict damage, but can momentarily stun the playable character. After a while, the Boo will disappear, though without earning the player points.

Unlike the normal Boos, attack type Boos can hurt the player like regular enemies. These Boos will float around normally until they spot the player and will start chasing them down. Should they reach the playable character, they will either hold them in place for other enemies to attack them, or attack directly. While just touching an attack type Boo will damage the player, defeating one will earn the player 300 points.

Throwing objects at these enemies will not affect on them, and when defeated in battle, the Boos release neither Animals or Chaos Drives

Sonic Lost World
In the Wii U version of Sonic Lost World, the Boos and Boom Boos appear exclusively in Sky Road Zone 4. In this game, the Boos are indestructible obstacles that move left or right across the screen in long rows and cause damage when touched. The player has to avoid them using the Magenta Rhythm Color Power.

Sonic Runners
In Sonic Runners, Boos appear as stage hazards in the Desert Ruins special stage.

Boom Boo
Boom Boo is large variation of Boos who also first appears in Sonic Adventure 2. Boom Boos look identical to normal Boos, but are able to evaporate three times larger after taking damage or shrink down after being defeated and eventually become attack-type Boos.

Sonic X
Both normal and attacking type Boos along with King Boom Boo appear in episode "Sonic's Scream Test" of Sonic X anime. Boos behave differently from their game counterparts and they live inside the old, abandoned castle in the middle of the lake instead of Eggman's large pyramid base. They also made laughing noises inside the old castle. Instead of choking others to attack, they possess the host as eyes and mouth change similar to Boo's.

During the episode, one of cameraman of the filming group takes hourglass statue from it's place that releases Boos out of vortex with unknown energy. During the first night Boos start to appear around, as taking the sound editor of the filming group and Lindsey Thorndyke to the vortex. In next night, Boos try to take Amy, Cream, Cheese and Ella. Tails and Chris shows up and manage to save Amy while rest of them got into the vortex. Sonic also arrives with hourglass on his hand and tries to attack Boos. He misses, but manages to break the rock door, revealing vortex in front view. However Tails and Sonic got caught, but Sonic manages to throw hourglass statue to Chris, and tells to him to return to it's altar. The rock door starts to fixed itself, thus logging the path to vortex.

Next day as Chris and Amy find out the another path to the vortex, Boos starts to attack them, but got scared away by hourglass statue on Amy's hand. Chris and Amy follow them to the room below the vortex. After being to told to insert hourglass statue to the small hole with Moon symbol on the statue facing upwards, King Boom Boo and Boos got free from the vortex. As Amy gets caught, one Boo takes the control of her mind. Amy then attacks Chris, while other Boos are laughing. However Chris switches the Sun symbol on the hourglass statue to face upwards and frees Sonic and others from the vortex, while Sonic karate-chops Boo out Amy's body. Amy joins the fight, as five Boos start to fuse to the larger Boom Boo, but gets easily defeated. After escaping from the under the castle, King Boom Boo and all Boos to get locked up the castle after Chris inserting the hourglass statue back to it's place.

The Boos would later return in the Sonic X comics in Issues #13 and 14, again seeking to escape into the real world. To this end, they sought to possess others like they had Amy, and succeeded in doing so with Lindsey Thorndyke and Vanilla the Rabbit. However, they were eventually convinced to return to their rest and leave the world of the living in peace.

Trivia

 * Before Sonic Adventure 2, there have been similar ghosts enemies called Hyudoros, which act similarly like Boos and are featured inside the pyramid at the second act of Sandopolis Zone in Sonic & Knuckles. Despite these facts, both Boos/Boom Boos and Hyudoros can be consider as separated ghost species.
 * Boo shares its name with enemies from the Mario series.
 * Boos' name in eyecatch card of Sonic X is spelled mistakenly as Boom.