Shadow

(from 5th Edition Monster Manual - 2014):

Shadows are undead that resemble dark exaggerations of humanoid shadows.

Dark Disposition. From the darkness, the shadow reaches out to feed on living creatures’ vitality. They can consume any living creature, but they are especially drawn to creatures untainted by evil. A creature that lives a life of goodness and piety consigns its basest impulses and strongest temptations to the darkness where the shadows hunger. As a shadow drains its victim’s strength and physical form, the victim’s shadow darkens and begins to move of its own volition. In death, the creature’s shadow breaks free, becoming a new undead shadow hungry for more life to consume.

If a creature from which a shadow has been created somehow returns to life, its undead shadow senses the return. The shadow might seek its “parent” to vex or slay. Whether the shadow pursues its living counterpart, the creature that birthed the shadow no longer casts one until the monster is destroyed.

Undead Nature. A shadow doesn’t require air, food, drink, or sleep.

(from 3.5e Monster Manual I - 2003):

This creature seems to be nothing but a patch of mobile gloom, more or less humanoid in shape. 

Shadows are creatures of sentient darkness, hating life and light with equal fervor. Their touch bestows the painful chill of nonexistence, making them very dangerous opponents. 

A shadow can be difficult to see in dark or gloomy areas but stands out starkly in brightly illuminated places. 

Natural enemies of all that live, shadows are aggressive and predatory. They are quick to strike and make short work of those unprepared to deal with them. 

A shadow is 5 to 6 feet tall and is weightless. 

Shadows cannot speak intelligibly. 

Combat: Shadows lurk in dark places, waiting for living prey to happen by. Strength Damage (Su): The touch of a shadow deals 1d6 points of Strength damage to a living foe. A creature reduced to Strength 0 by a shadow dies. This is a negative energy effect.

Create Spawn (Su): Any humanoid reduced to Strength 0 by a shadow becomes a shadow under the control of its killer within 1d4 rounds. 

Skills: Shadows have a +2 racial bonus on Listen and Spot checks and a +4 racial bonus on Search checks. 

*A shadow gains a +4 racial bonus on Hide checks in areas of shadowy illumination. In brightly lit areas, it takes a –4 penalty on Hide checks. 

Greater Shadow: 

Although no more intelligent than an average shadow, a greater shadow is more fearsome because of its increased damage and its hit-and-run tactics.

Combat: A greater shadow uses stealth and cunning in combat. A favorite tactic is to lie in wait, almost completely concealed by walls or floor, then swoop out, make an incorporeal touch attack, and retreat back into a solid object without allowing a return attack. 

Strength Damage (Su): The touch of a greater shadow deals 1d8 points of Strength damage to a living foe.

(from 2e Monstrous Manual - 1993):

Shadows are shadowy, undead creatures that drain strength from their victims with their chilling touch.

Shadows are 90% undetectable in all but the brightest of surroundings (continual light or equivalent), as they normally appear to be nothing more than their name would suggest. In bright light they can be clearly seen.

Combat: As shadows exist primarily on the Negative Material Plane, they have the ability to drain the life force of their victims. The chilling touch of a shadow inflicts 2-5 points of damage to its victim as well as draining one point of Strength. Lost Strength points return 2-8 turns after being touched. If a human or demihuman opponent is reduced to zero Strength or zero hit points by a shadow, the shadow has drained the life force and the opponent becomes a shadow as well. The newly formed shadow is then compelled to join the roving band and pursue a life of evil. Other living creatures simply collapse from fatigue (if taken to zero Strength) or fall unconscious (if taken to zero hit points), where they are left to die or are hounded again upon waking.

Shadows are immune to sleep, charm, and hold spells and are unaffected by cold-based attacks. They can be turned by clerics.

Habitat/Society: Shadows travel in loosely organized packs that freely roam ancient ruins, graveyards, and dungeons. They specialize in terrifying their victims.

Shadows have no leaders and thus spend much of their time roaming aimlessly about their chosen surroundings. Contrary to popular belief, shadows do not hoard treasure. In fact, such earthly baubles only help to remind the creatures of their former lives. Instead, the furious undead throw all of the treasure they find away, in the same location (often at the bottom of a well or deep pit), where it is out of sight of the band. It is therefore speculated that the removal of a shadow hoard would be quite easy (even welcomed), were it not for the fact that shadows attack living beings without hesitation, regardless of their intent or threat.

Ecology: According to most knowledgeable sages, shadows appear to have been magically created, perhaps as part of some ancient curse laid upon some long-dead enemy. The curse affects only humans and demihumans, so it would seem that it affects the soul or spirit. When victims no longer can resist, either through loss of consciousness (hit points) or physical prowess (Strength points), the curse is activated and the majority of the character's essence is shifted to the Negative Material Plane. Only a shadow of their former self remains on the Prime Material Plane, and the transformation always renders the victim both terribly insane and undeniably evil.

Attempts to remove the curse from captured shadows have all failed, thus providing more clues into the nature of the disorder. A limited wish spell proves only partially successful as the victim returns for an hour but remains insane for the duration. It has been recently speculated that a full wish, followed by a heal spell, might be capable of restoring a shadow to his former state, but again it must be emphasized that this is only a theory.

Fortunately, shadows rarely leave their lairs, and a bold party wishing to rescue a lost fighter or wizard should have plenty of time to venture forth and recover their friend, provided that no one else explores the lair and slays the unfortunate character while the shadows are absent.

The original body of a victim is destroyed when changed to a shadow whether by the curse itself or by unprotected exposure to the Negative Material Plane. In any case, killing a shadow is merely a case of severing the bond between the Prime Material and Negative Material forms.