Negative energy

Negative energy is a broad category of spells and effects. It could also be called Death energy. All Inflict spells channel negative energy. All undead exist because of negative energy which is why they are damaged by "healing" (or life energy) spells and "healed" by Inflict spells.

The following effects are negative energy effects:
 * ability damage/drain
 * negative levels
 * inflict/harm spells
 * most Necromancy spells, such as enervation and ray of enfeeblement

These effects can be avoided by the Death ward spell except the ability drain effect of some undead monsters.