What would a Greater Doppelganger's Cr be? Using the article in Monsters of Faerun pg 35.
Str 2; Dex 6; Con 2; Int 6; Wis 6; Cha 2
They can Detect Thoughts continuously
Polymorph Rend: Deals 6d6 to a polymorphed, shapeshifted, or polymorphed other creature.
Alter Self
Can use UMD no matter what class he is mimicking.
And of course the Consume Identity is their bread and butter, they can eat the brain of a person and become 100% like them, learning memories, etc even Class levels and features (So long as you are in their morph)
If you do something against someone's alignment you are kicked back to base form for 1d10 turns.