Unari’s Cauterizing Flame

You bind unstable hellfire to a single creature, sealing its fate within accelerated time.

Choose one creature within range. That creature must make a CON save. Target takes 6d8 fire and 6d8 necrotic on a failed save, or half as much on success. At the start  of each of the target's turns it takes 3d8 fire and 3d8 necrotic.

This fire ignores fire resistance and treats fire immunity as resistance. 

If target's Hp drops to 0, the spell ends early.

If your concentration is broken, the flame violently collapses, causing Creatures within 10 feet of the target take 4d8 fire damage.