This is a Cyclopedia Bestiary Entry from Pillars of Eternity

Monster Name: Shadow

PillarsofEternityBestiaryShadow.jpg

Shadows are created when creatures with heavily fractured souls die without re-entering the cycle of rebirth. Because these souls are damaged, they drain essence from other creatures in a futile attempt to repair themselves. The more essence they steal, the more powerful and dangerous shadows become. As they devour essence, they pick up pieces of corporeal matter, giving them a visible, if indistinct, form. Luckily, shadows can only draw a small bit of spiritual energy from souls still attached to a body or bound to an object. They mainly rely on creatures like the pŵgra, who can draw souls out of their physical form, to help them obtain the essence they crave.

Shadows have been known to draw spiritual energy from people while they sleep, when their souls are not bound as strongly to their bodies. This results in horrible nightmares that leave the person in an exhausted state the next day. If an entire town suddenly begins to suffer nightmares, it is highly probable that a strong shadow has taken up residence there.

Since shadows absorb spiritual energy, they appear invisible to creatures that rely on spiritual sight. This has led to experiments in binding shadows to armor or other objects to act as a cloak to obscure those who do not wish to be seen by such creatures.