Thorn skin

You touch a willing creature. Until the spell ends, the target's skin has a rough, bark-like appearance with hard thorns sticking out of it, and the target's AC can't be less than 16, regardless of what kind of armor it is wearing, if the target is not wearing armor then any unarmed strikes against the target result in 2 d4 piercing damage. the same result can be achieved by the target of the spell using an unarmed strike against an enemy.