Vindictive Sheen

Concentration Spell. Create a thin shimmering coat over yourself. This shimmering coat starts off as a translucent red, but becomes steadily brighter until the spell ends. Adds +3 to your Armor Class for the duration of the spell, and once the spell ends, (if Concentration drops or 3 rounds pass) the sheen will explode, creating a bright red flash of light within 15 feet, causing every creature to roll a Con. Saving Throw. If they succeed, half damage. If they fail the saving throw, they receive 1d10 force damage per rounds the Vindictive Sheen lasted before exploding (if it lasted till 3 rounds, it deals 3d10. If Concentration broke after the 1st round, 1d10).