No. Enc.: 1
HD: 5 (d12)
Move: 30 ft
Attacks: Grapple (1d6)
Special: Reduced Demon Abilities,
Mirror Travel, Energy Drain,
Change Shape, Class Abilities,
Saves: P, M
Align: Chaotic Evil
TR: Nil (but see below)
A mirror demon is a lesser form of True Demon that can travel from the Abyss into the mortal plane via any mirror large enough for to allow their bodies to pass through. They may take the form of those they kill, and they greatly enjoy creating havoc and discord among the family and friends of their victims. They prefer to target the vain and beautiful (the types of people prone to stare at themselves in a mirror extensively). In their true form, their skin is pale (almost corpse-like), with jet-black eyes that cry tears of blood.
A mirror that a Mirror Demon has recently used to travel through, or observe their potential victims, will glow faintly of demonic magic if subjected to a Detect Magic or Detect Evil spell.
Although the demons have no treasure themselves, their victims are often wealthy (the poor being highly unlikely to own a mirror large enough that the demon could pass through).
Combat: A mirror demon will usually wait until their victim is alone in whatever room the mirror is in, with their guard down, before traveling through the mirror to attack. They will grapple (literally trying to to choke the life out of their victim), with successful attacks also leading to the victim being Energy Drained (see below).
Reduced Demon Abilities: Mirror Demons have the following standard demonic abilities: Darkvision 90', immunity to electricity & poison, and taking only half damage from acid, cold, & fire. They also have a spell Resistance of 20, and the standard demonic empathy/telepathy which allows them to learn the thoughts, and speak any language known, of their victim, although they must observe their victim at least three times within a week's span through a mirror before this last ability is granted.
Mirror Demons are not immune to non-magical weapons, nor do they possess the standard demonic ability to Teleport or Gate.
Mirror Travel: Mirror Demons can travel between the mortal plane and the Abyss via any mirror large enough for them to fit through. Even if a mirror is too small for them to pass through, they can still see and hear through them, observing their potential victims and learning about them via the above-mentioned empathy/telepathy ability. Note that mirrors in areas that have been Consecrated or Hallowed are barred to the Mirror Demon.
Energy Drain: In addition to suffering the above normal damage, living creatures successfully hit by a Mirror Demon’s attack lose one level. These losses are permanent, and can only be regained by the use of a Restoration or a Wish spell. If the victim is slain, this also allows the Mirror Demon to use their Change Shape ability, and to use the Class Abilities that they have drained (see below).
Change Shape: Any victim slain who was also the subject of a Energy Drain can then be mimicked by the Mirror Demon, in a manned similar to a Doppleganger. The Mirror Demon can maintain the victim's form indefinitely, until they take the form of another victim, or they travel back to the Abyss via Mirror Travel.
Class Abilities: Any character levels drained via Energy Drain may be used by the Mirror Demon to further the pretense of taking the role of their victim (up to 6th level). These extra levels do not alter the Mirror Demon's hit points, and are subject to the same duration limitations as their Change Shape ability.
Reflection Weakness: Although their Shape Change ability is otherwise nearly flawless, their true form can always be seen if they are observed through a mirror, or anything else that will cast a reflection (such as the still waters of a pond).
Note: AD&D-style demons have not (as far as I know) been officially covered in the C&C rules - I based my write-up on the unofficial Creatures Features fan-supplement, which can be downloaded here (my XP value is higher than many of the equivalently-dangerous demons, as it appears to me that many XP values for monsters - official and otherwise - don't fully account for all of a monster's abilities)