The Doppelganger is a pitiful creature. They are born human with the ability to switch their appearance but many Doppelgangers, with time, lose their sense of who they were. The most unfortunate ones become mad and grotesque in appearance.
Sizes for physical copies are measured from foot to eye-level of a standing human miniature (e.g. Human Warrior at 32mm to eye-level, Goblins/Dwarves slightly smaller).