Vitriol's Obsidian shield

A ring of four magic obsidian spheres appear rotating around your person or a person of your choosing. Because they are rotating around you, your ac is now increased by 1d6 for 2 minutes after cast or until you run out of spheres. You are able to launch them one at a time as an action dealing 2d4 damage on a hit with a range of 90 ft. If you are attacked while you still have spheres up you are able to sacrifice 2 spheres to reduce the attack by 1d4 if its ranged and 2d4 if its melee.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d4 for each slot level above 2nd. The number of spheres also increases by 1 for each slot level above 2nd.