NEUS Projects

Can the Ghost Dog, headless knight, and the tainted soul of darkness count as undead monsters? They'd be weak to the holy enchant and also would count as undead monsters while doing the laplace quest Slaughter the Undead.

They technically aren't undead. Ghost Dog and Soul of Darkness are ghosts. Headless Knight is a Dullahan, so it counts as Possessed Race.

They aren't undead, so no.