Elixir of Spike Skin

Slivers of bone float in the viscous, gray liquid inside this vial. When you drink this potion, bone-like spikes protrude from your skin for 1 hour. Each time a creature hits you with a melee weapon attack while within 5 feet of you, it must succeed on a DC 15 Dexterity saving throw or take 1d4 piercing damage from the spikes. In addition, while you are grappling a creature or while a creature is grappling you, it takes 1d4 piercing damage at the start of your turn.