Cataclysmic Fire

You hurl a mass of violet flames to a point you choose within range.  Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 5d6 fire damage and 5d6 necrotic damage on a failed save, or half as much damage on a successful one.

Additionally, any Medium or smaller Humanoid killed by this damage, as well as every corpse of such a creature within the sphere, becomes a skeleton under your control. The skeleton acts on your initiative but immediately after your turn. It obeys any verbal commands that you issue to it (no action required by you). Absent any other command, the skeleton tries to kill any non-Undead creature it encounters.

At Higher Levels. When you cast this spell using a spell slot of 8th level or higher, the fire damage or the necrotic damage increases by 1d6 for each slot level above 7th.