Bloody Dome

A rather unsettling spell, it creates a red-hued dome with a radius of 20 feet at a point within range. As an action you can cause the dome to forcibly implode on itself. Creatures caught within the dome must make a Constitution saving throw or take 4d6 necrotic damage, or half as much on a success. The damage of this spell increases by 1d6 for each living creature in the area of the dome when it collapses; these creatures must be tiny or larger. 

If you lose concentration on the spell, the dome harmlessly dissipates, dealing no damage.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher the radius of the sphere increases by 10 feet for each slot level over 3rd.