Vermontis Demonic Rapture

This spell summons a swarm of floating possessed skulls from hell, that fill a 30 foot cube within range. Each creature who starts or ends their turn in the area is relentlessly attacked by the skulls, each creature has to make a dexterity saving throw. On a failed save they take 5d8 necrotic damage and movement speed is reduced by 15 feet until the end of there next turn, on a successful save they take half damage and speed is reduced by 5 feet. And any attack that deal necrotic damage deals an extra 1d10.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the size of the cube increases by 10 feet, and the skulls deal an extra 1d8.