Boo is very shy and somewhat intelligent. He studies a lot, leading Yoshi to call him a bookworm. Most of the time, he agrees with what Paratroopa has to say about Yoshi's witty remarks and plans to evade boredom.
Unlike other Boos, he doesn't hide his face when something or someone looks at him. He can keep his vast collection of books in his mouth, which is implied to be a portal that leads to another dimension. He is also able to use some forms of magic, like pyrokinesis.
Before he became a Boo, he was a Spike Top who worked for Bowser. He got game-overed by Luigi in the Bland Sand Mansion after he was touched with a Shiny Star. Later, he re-joined Bowser's ranks as a Boo. Later on, he got teamed up with Paratroopa in a few reconaissance missions. After they decided to leave the Koopa Troop, he and Paratroopa met Yoshi and stopped the Koopa Troop's attack, which is how they became best friends.
During the beginning of Chapter 1, Boo is hanging out with Yoshi, sharing in his boredom.
He appears in Chapter 4 after he is transported to Dreamland by Dark Matter. Dark Matter put a remote on his hand, but he gave it to Kirby and pals. In Chapter 5, he and the other two sang a song and got bagged afterwards. He also states to like Li'l Gordo and his dance group.
-Boo is able to get things by pulling stuff out of his mouth, which may be a portal to another dimension.
-He hates light, as it paralyzes him and he usually drops to the ground afterwards.
-He used to go to school with Kirby.
-He hates the Spies in Team Fortress 2, as he constantly gets backstabbed by them.