Wraith

Incorporeal, undead monsters that appear as pale, human-like forms of coalescing mist. Dwell in deserted regions or in the homes of former victims.

AC3 [16], HD4** (18hp),
Att 1 × touch (1d6 + energy drain), THACO 16 [+3],
MV 120’ (40’) / 240’ (80’) flying, SV D10 W11 P12 B13 S14 (4),
ML 12, AL Chaotic, XP 175, NA 1d4 (1d6), TT E

• Undead: Make no noise, until they attack. Immune to effects that affect living creatures (e.g. poison). Immune to mind-affecting or mind-reading spells (e.g. charm, hold, sleep).
• Mundane damage immunity: Only harmed by silver weapons or magic.
• Damage reduction: Half damage from silver weapons.
• Energy drain: A successfully hit target permanently loses one experience level (or Hit Die). This incurs a loss of one Hit Die of hit points, as well as all other benefits due to the drained level (e.g. spells, saving throws, etc.). A character’s XP is reduced to the lowest amount for the new level. A person drained of all levels becomes a wraith in one day, under the control of the wraith that killed them.

Source: Classic Fantasy