Energy Release

The caster releases a portion of their essence in a 50ft radius, dealing 10d10 necrotic damage to all enemies in range. For every three enemies hit, the caster takes 1d4 necrotic damage as well. As an action whenever you change positions, you can move the sphere with you; and all enemies must succeed on a CON saving throw of 18 or take another 10d10 necrotic damage; and half as much on a failed one.

(This spell deals an extra 1d10 and 1d4 necrotic damage for every level above 7.)