Dopplegangers are weird humanoid creatures who are able to take on the appearance of nearly any other humanoid ranging from 3 feet up to 7 feet in height. They can also read minds (as the spell, mind reading, but with unlimited duration), an ability that can even be used to speak any language known to the creature whose mind is being read. In their natural form (which few creatures ever see) they are pale and pasty looking, slim, around 5½ feet tall and weighing about 150 pounds. Their features look unformed and incomplete.

Dopplegangers wish to live a life of ease, and in pursuit of that goal they will seek to take the place of any character they meet who they believe can help them get that kind of life. This usually means separating the victim from any allies and quietly killing them. While a doppleganger can duplicate the appearance of the clothing and equipment worn by a creature, such items are part of the creature and cannot, for example, be laid down or handed to someone. Taking the clothing and equipment of a victim is thus the preferred tactic.

A doppleganger can mimic the sound of the voice of any living creature as well as the appearance of any humanoid. Their mind reading ability will be used to help them behave like the person they have replaced.