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Ghoul Guys are gray Boo Guys that appear in the Shroob Castle in Mario & Luigi: Partners in Time. Their attack is a quicker and stronger version of Boo Guys' attack. Ghoul Guys can roll into Mario or Luigi, inflicting damage. Before a Ghoul Guy attacks, it splits into two transparent copies, including a fake copy. Only the real Ghoul Guy attacks. Before attacking the Ghoul Guy points to the character it will attack.
Unlike Boo Guys, Ghoul Guys can merge with another enemy. The Ghoul Guy is defeated, and the enemy affected has all of its stats increased. This is similar to Peps in Mario & Luigi: Bowser's Inside Story.
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