Boos (ブー Bū) are a species of white-hued ghosts found all over the world in Sonic the Hedgehog games, primarily in ancient areas such as temples or tombs. They are known to be servants of King Boom Boo and come in two very different variations: Normal Boos have black, beady eyes and a mouth which has been stitched closed; the second type instead have wild, reddish-orange eyes and sharp black teeth. They also appear in two different sizes, with larger variants being referred to as Boom Boos, although a Boom Boo can appear as either of the aforementioned types. It is noted however that the "unrestrained" Boos tend to be larger than those who have been stitched up and are much more energetic and violent than their kin.
Boos of all types seem to be a mischievous lot, and have been known to hide inside of gravestones, pumpkins and even just within the ground itself. Boos which do this will suddenly pop out to startle and stun a victim yet for some reason will not attack afterwards. Those who are more malicious and do attack however will often do so in one of two manners:
- Grab their victim and hold them in place while another enemy gets a free shot at the individual, or
- Choke their victim themselves.
Boos are completely immune to having objects thrown at them, as they will simply dematerialize and let it pass through them while continuing to pursue their targets. As Boos are simply ghosts and not one of Dr. Eggman's creations, none of the Boo types contain Animal Friends nor Chaos Drives to collect. They may also be somewhat related to Hyudoros, although the two ghost types are stated to be separate species.
- Sonic Adventure 2 (first appearance)
- Pumpkin Hill (Knuckles)
- Aquatic Mine (Knuckles)
- Death Chamber (Knuckles)
- Pyramid Cave (Sonic)
- Egg Quarters (Rouge)
- Sonic Adventure 2 Battle
- See above
- Sonic X
- Sonic Lost World
- Desert Ruins