Briarskin

You touch a willing creature. Until the spell ends, the target's skin has a rough, bark-like appearance, and the target's AC can't be less than 16+(your)WIS, regardless of what kind of armor it is wearing. As a reaction to taking damage from an adjacent creature while briarskin is active, you may have that creature make a DEX saving throw or suffer 3d6 points of piercing damage as the thorns in your armor spring out and lash at your target.