Xykon's Energy Drain

Necromantic energy washes over a creature of your choice that you can see within range, draining the life force and arcane energy from it. The target must make a Constitution saving throw. The target takes 10d12 necrotic damage on a failed save, or half as much damage on a successful one. This spell has no effect on undead or constructs.

If you target a spellcaster, on a failed save you can drain their spell slots, up to a combined level of 2d4. The spell slots are treated as if they had been used.