Thorn Armor

When you cast this spell, a flexible exoskeleton covered in thorns appears around a willing target within range. The target gains 3d6 Temporary Hit Points. If a creature hits the target with a melee attack roll before the spell ends, that creature takes Piercing damage equal to the number of Temporary Hit Points lost as a result of the attack. This spell ends early if the target has no remaining Temporary Hit Points granted by this spell.

Using a Higher-Level Spell Slot. The target gains an additional 2d6 Temporary Hit Points for each spell slot level above 1.