For the Super Mario Bros. enemy, click here.
Boos all have white, spherical bodies with a pair of small arms that have clawed fingers. They also have manic-looking eyes with yellow irises on red sclera with dark rings around them. Their mouths are filled with black, dagger-like fangs. They also have a calm side; when they are calm, they have black, soulless eyes, their mouths are knitted-up, and their arms are thin like paper. Despite they had a short tail, their tails can be very long as their bodies can stretch in a long size.
Boos are playful, energetic and fun-loving, as they like flying around and possessing people. They will giggle and laugh as they have fun with people or cause misdeeds.
Boos are mischievous and sneaky. In some cases, they can be plainly seen and will advance on a victim menacingly. Other times, they will lurk in the shadows or inside objects, bursting out to frighten a victim when they approach. As shown in the Sonic X anime series, Boos are also capable of possessing people and will manipulate their victims into attacking their friends. They have elastic arms, so they can stretch their arms out to great lengths and catch their victims.
- Boo are named Boom in Sonic X.
- Despite with female voices, Boos are rather genderless.