- Spectres "drain two life energy levels each time they score a hit."
- Vampires "drain two life energy levels, as do spectres, when they hit an opponent in combat."
- Wights "drain away life energy levels when they score a hit in melee, one level per it."
- Wraiths "drain life energy, 1 level per hit."
Now conventional wisdom has it that, like with hit points, once your character's level falls to zero, he's dead. However, what about "normal men"--also known as zero-level characters? Obviously one hit from a level-draining undead is going to take out your man-at-arms. But should that apply to a first-level character who is drained of a single life energy level? Or is he not quite "totally" drained of vitality?
I say no, and there's precedent in the rules to support me: the "normal man" that appears in the combat and saving throw tables. A first-level character who has one level drained away, or a second-level character who loses two levels, becomes a 0-level "normal man" (whatever the PC's original race and class) for game purposes. Any hit that takes a character below zero-level, of course, slays that individual and turns him or her into the same type of undead that slew the character.
This means using the appropriate line on the to-hit and save charts, and not being able to use class-specific abilities like spells or thief skills. Why do this? First of all, it keeps your brand-new first-level character alive after a hit from a wight, even if at very reduced capability, and therefore gives the entire party a greater chance of surviving the encounter. Second, it provides new opportunities for adventure in search of a cure, as you can let the players know that there's a certain temple which can restore the lost vitality (for a price, or in return for a quest), or have them meet a ranger who knows how to make a potion which can heal their affliction. You could even be merciful and allow that several weeks of rest, plus a certain amount of experience points (say, one-fourth of what it takes to reach second level), gets them back up to first level.
Whatever method you choose, these ideas allow low-level characters to survive encounters with level-draining undead. When they recover, they'll be ready to hit the dungeon again, and hopefully be a little more careful this time.