Aghar's Elder Barkskin

You touch a willing creature. Until the spell ends, the target’s skin assumes a bark-like appearance, and the target has an Armor Class of 17 if its AC is lower than that. Additionally, damage taken from Bludgeoning, Piercing, or Slashing Damage is reduced by 2. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the Armor Class granted increases by 2 and the damage reduction increases by 1 point for every two slot levels above 2nd