Death Fog

When you cast this spell, a pale fog rises from the ground to fill a 20-foot-radius sphere at a point you can see within range. Each round a living creature begins its turn inside this fog, they must roll a Constitution saving throw or suffer 3d10 necrotic damage. The fog changes color to become increasingly dark red the more damage it inflicts.

As an action, you can move the fog cloud up to 60 feet, but if it moves out of range, the spell ends immediately.

Any round you or any of your chosen allies start their turn within the cloud, you each gain 3 temporary hit points, but only if the cloud inflicted damage on enemies in a previous round.

If the spell is cast a higher level, the damage increases by 1d10 per level.