To get a better handle on a character I'm working on, I've decided to try to stat out his heritage, ie. the doppleganger as a supernatural species.
The doppleganger is a supernatural creature known to temporarily assume the identity of mortals in order to carry out its nefarious ends with impunity. They are the quintessential identity thieves. While some monsters might kill, eat, or otherwise assault a mortal to 'steal' their identity, the doppleganger is far more insidious. A few casual words with one is often enough for it to create a passable disguise. Much more, and they'll begin to accomodate your various identifying mannerisms and even learned skills into their disguise, until even your most intimate acquaintances won't be able to tell the difference.
Dopplegangers are almost universally evil, frequently murderous, and predominantly of greater-than-human-average intelligence, though they vary from one individual to another as with any species.
They are almost never encountered in groups, but when they are, they are typically mate-pairs, and far more likely to resort to lethal forms of amusement.
Musts:
True Shapeshifting (with compels when necessary to forbid non-humanoid forms, but leaving the skill-shifting intact)
Modular Abilities: typical building block powers, creature features as appropriate (possibly Limitation to force the assumed powers to be suited to the assumed form)
Supernatural Sense granting the ability to see things for what they are (safer, but less potent version of the Sight)
some mind-reading capability; possibly Telepathy from the custom powers list, possibly just another Supernatural Sense
Minimum Refresh Cost: (9 or higher, depending on the telepathy option)
Options: additional Form Points; building block powers independent of Modular Abilities (and thus independant of the assumed form); Telepathy upgrades (if using that custome power)
Rejected powers:
Mimic Abilities: the incredibly circumstance-dependent potency of this power, combined with its unsuitable built-in Limitation make it less than ideal
Mimic Form: a similar built-in Limitation renders this similarly unsuitable
The Sight: I like to keep this potent ability reserved for Practitioners and 'higher beings' such as various angels with the ability to 'judge the worth of one's soul', but monstrous species spending most of their lives in forms other than their own, particularly in a world where other monstrous species might be doing the same, are bound to develop some sort of similar capability
Ideas? Comments? Suggestions?