AG's Boon of the Black Mist

You have immunity to Acid and Poison damage. Additionally, if you would take more than 25 Acid or Poison damage from any single source, summon a 25ft noxious cloud of fog around yourself. The fog has the following effects.

• At the start of your turn, creatures of your choice become heavily obscured while within the area until they attack or cast a spell. You cannot obscure yourself with this effect, and it lasts until you take damage.
• When an obscured ally is damaged by an attack or spell that didn’t damage you, your next attack or spell deals an additional 20 poison or acid damage on a successful hit or failed save.
• You must use your bonus action to maintain this effect, and it cannot be activated again for 5 minutes once deactivated. The effect ends automatically after 1 minute.