"Their life energy may be pure and tasteless, but it sure feels good!"Life Drain is a second-level Death Magic spell in Heroes of Might and Magic IV that costs three spell points and steals hit points from all Life and Nature creatures in battle and gives some of them to the caster as healing.
An unusual spell, Life Drain fills two roles not otherwise found in Death's arsenal: area-damage, and healing.
As an attack spell, the damage is not usually sufficient to affect any but the smallest battles. Death is usually much better served focusing on its debuffs: Unholy Song is a much better choice against Life units, and, with the exception of Elementals, Nature units are susceptible to all of your other curses, leaving you many superior options against them as well.
That having been said, while the limited choice of target alignments means that you cannot afford to rely on it as anything but a serendipitous source of healing, it may occasionally be useful.