Adamantine Echo

You unleash a thunderous roar to batter your enemies, and scales like those of an adamantine dragon cover your skin. You explode in a thunderous wave and every creature within 15ft of you must make a CON save. If they fail they take 4D6 thunder damage and keep taking an additional 5 points of damage every turn until they succeed on the save. They can do the save at the end of there turn. Half damage if they succeed on the first save and no on going thunder damage. You also gain a boost to your AC equal to your Dex modifier until the end of the encounter.