Doppelgängers take the form of other people in order to fool them, and emulate some of their abilities to a lesser degree.
Steal Form
As a swift action you can transform into an enemy you can see within line of sight, or that you have seen within the last minute. While shifted into this enemies’ form, you can take advantage of key features.
Class: If the enemy is a creature with class levels, you can emulate one of their class features, so long as the class feature is of a level equal to your level - 1 or lower. This class feature, if it possesses a “uses per day” or something similar, this is restricted to once per day. This also applies to “per encounter” or other use-limited abilities.
Species Ability: If the enemy is a creature that solely possesses levels in their species (this applies primarily to Bestiary monsters), you can emulate one of their species abilities. Their EL must be equal to your level - 1 in order to do this.
This replaces Form Shift.
Mental Shield
This function as per Natural Resistances, except it applies to Mental Defense instead of Bodily Defense, and against enemies’ mind-affecting effects.
This alters Natural Resistances.
Master of Disguise
You receive a +1 bonus to Deception per level of Mental Shield (maximum of +6 at 18th level), this bonus is doubled while using Steal Form.
This replaces Natural Defenses.
Doppelgänger Aspect
4th Level: You can alter your voice while transformed, gaining a +10 to sound-only based Deception checks made to pretend to be the form you’re disguised as.
8th Level: Enemies with a Smarts score who notice you have transformed into them take 1 Sanity damage. This can only be triggered once per day.
12th Level: You add the following spells to your spell list and count them as Nature spells; Illusory, Size Alteration, Destabilize, Infuse Power, and Break the Body. You still must be the appropriate levels to cast these spells.
16th Level: You reroll 1s and 2s on Deception checks, as well as causing 9s and 10s to explode.
20th Level: You are immune to critical hits and called shots.
This replaces Animal Aspect.
Hardened Mind
You are immune to enemies’ mind-affecting effects, and double the bonus to Mental Defense from Mental Shield except it applies against any effect to Mental Defense.
This replaces Hardened Immune System.
Unchained Awakening
Increase HP while using Steal Form, this bonus HP is equal to double Luck.