Boo Guy

A Boo Guy is a Shy Guy ghost that first appeared in Super Mario World 2: Yoshi's Island. Like their corporeal counterparts, Boo Guys emerge from pipes and wander around back and forth to attack. Additionally, some Boo Guys are stationed inside castles, operating mechanical traps to stop Yoshi and his friends. Some drop giant spiked balls on the dinosaur heroes, while others operate long, spiked weapons that travel in a circular path. Some Boo Guys even drop missiles, creating explosions to harm Yoshi and his allies.

Boo Guys also appear in Mario & Luigi: Partners in Time. In this game, Boo Guys reside in Toadwood Forest. Instead of wandering around aimlessly or operating machinery, these Boo Guys attack by rolling into Mario or Luigi. However, before a Boo Guy attacks, the ghost will split into two transparent copies: one real, one fake. Only the real Boo Guy can harm Mario or Luigi. Thankfully, Boo Guy will point to the Mario brother he will attack, meaning the brothers should not be caught off guard by the illusionary Boo Guy.

Boo Guys made a return with better graphics in Yoshi's Island DS.