Crystal Armor

You create an armor of glistening crystals on your body. This armor increases your AC by 1 for the duration. If a creature hits you with a melee attack while you have this armor, the creature takes 1d8 piercing damage, a creature can take this damage a maximum of once per turn.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the piercing damage increases by 1d8 for each slot.

From the Feywild Spellbook by E. R. F. Jordan, all credits to them.