Bone Splinter

You divide bones into splinters and create a flexible cuirass to protect yourself. Your AC increases by 5 and you become resistance to non-magical bludgeoning damage while this spell is active. Your movement speed is also reduce by 10 feet. Whenever an enemy hits you with a melee or ranged attack, parts of the bone break off, reducing your bonus AC by 1. When the total bonus AC is reduced to 3, you lose resistance to non-magical bludgeoning damage, but your movement speed is no longer halved. You can take damage 5 times until the armor wears off completely. 

While your armor is active, you can use your action to magically dismantle parts of it and fire bone splinters at an enemy up to 60 feet away using a spell attack roll, dealing 2d6 piercing damage if it hits. You can do this up to 5 times in any turn, but each attack decreases your bonus AC by 1 until it is gone. These attacks do not expend additional spell slots.