Ghoul Guy

A Ghoul Guy is a gray Boo Guy, a Shy Guy ghost, that lives in Shroob Castle, the Shroobified version of Princess Peach's Castle. These incorporeal Shy Guys attack in the same manner as their Boo Guy counterparts. In battle, a Ghoul Guy will roll into Mario or Luigi, inflicting damage. Interestingly, before a Ghoul Guy attacks, the Shy Guy spirit will split into two transparent copies: one real, one fake. Like the Boo Guy, only the real Ghoul Guy can injure the Mario Bros. Thankfully, the Ghoul Guy will point to the Mario brother the ghost will attack, meaning the Mario Bros. should not be fooled by the illusionary Ghoul Guy.

Additionally, Ghoul Guys have a unique ability that Boo Guys don't possess; a Ghoul Guy can merge its spirit with another monster in the battlefield. Although the Ghoul Guy disappears from existence, the other monster will be infused with the ghost's power, greatly increasing the creature's stats. As such, Ghoul Guys should be destroyed before they can merge their essences with other enemies.