Holy Oil
Potion (oil), minor, common
While holy oil burns in a lamp or lantern, each fiend or undead creature within the bright light it casts takes one radiant damage at the start of each of its turns.
A cleric or paladin may create holy oil by performing a special ritual. The ritual takes 1 hour to perform, uses 50 gp worth of powdered silver, and requires the caster to expend a 1st-level spell slot.
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