Tiamat's Revenge

You touch a creature, and the creature instantly takes 20d10 Radiant damage, and 5d10 Force damage. If the target is a chromatic dragon, the target takes half damage, and if the target is a metallic dragon, the target takes an extra 10d10 Radiant damage. The target then must succeed on a Constitution saving throw or be poisoned until the end of your next turn. If the target is still at at least 1 hit point, roll a d6. The target's AC gets reduced by the amount rolled + 2.