Shuushin15 Nov 2003

Special Abilities: Detect Thoughts (Su): A doppelganger can continuously detect thoughts as the spell cast by an 18th-level sorcerer (save DC 13). It can suppress or resume this ability as a free action. If it can read an opponent's mind, a doppelganger gets a +4 circumstance bonus to Bluff and Disguise checks

Special Qualities: Alter Self (Su): A doppelganger can assume the shape of any Small or Medium-size humanoid. This works like alter self as cast by an 18th-level sorcerer, but the doppelganger can remain in the chosen form indefinitely. It can assume a new form or return to its own as a standard action. While using alter self, a doppelganger gets a +10 circumstance bonus to Disguise checks.

Immunities (Ex): Doppelgangers are immune to sleep and charm effects.

or

I recommend:

The Complete Guide to Dopplegangers

"The Complete Guide to Doppelgangers is a stand-alone, world-neutral sourcebook covering everything you ever wanted to know about doppelgangers. As a GM, you'll learn how to run doppelgangers -- both in combat and role-playing situations. And since every Complete Guide includes guidelines on playing the monster as a character race, players have new options, too. The Complete Guide to Doppelgangers features:
The true origin of these bizarre creatures.
Background on doppelganger social structure, including their various life stages and details on how they have penetrated human and demi-human society.
Unique campaign ideas and adventure hooks centered around doppelgangers.
New monster stats for intriguing variations on the standard doppelganger. "