Pathfinder 2e Item: Foe's Bane Frok

Porcupinebearskin Frock   When you take damage, the frock gains one charge, with a maximum of 5. Expend one or more charges when you succeed at a melee unarmed attack roll to deal an additional 1d8 piercing damage per charge spent.   When an enemy crits you with a melee attack, use your reaction and expend all your charges, dealing 1d8 piercing damage per charge spent to the enemy.   The wielder knows the direction and distance to enemies damaged by the spines fired on expenditure of a charge, until the victim succeeds a DC 20 Medicine Check to remove it.