Running a combination of 1e Against the Giants and 4e’s Revenge of the Giants. Found this little spell in the back of the 1e adventure. Converted to 5e. Very nasty spell.
Energy Drain
Casting Time: 1 action
Range: Touch
Components: V (“Entropy” or similar), M (essence of spectre or vampire dust)
Duration: Instantaneous
By casting this spell the magic-user opens a channel between the plane he or she is on and the Negative Material Plane, the caster becoming the conductor between the two planes. As soon as he or she touches any living creature, the victim gains 1d4+1 levels of exhaustion
On a critical hit, the amount of exhaustion is doubled. On a critical failure, the caster loses half as many levels of exhaustion. Humans or humanoids brought to zero energy levels by this spell become zombies.