Boo Guys

A photo of Boo Guys.

Boo Guy is variation of the common Mario foe Shy Guy. It appears to be a dead Shy Guy and can't be killed unless Mario is invincible. A variant of the species appears in Luigi's Mansion. They're called Shy Guy Ghosts.

Boo Guys also appeared in Mario and Luigi: Partners in Time. One subspecies of a Boo Guy is a Ghoul Guy.