Doppelgänger

Doppelgängers are beings that are one of the few true shapeshifters in the world.

Appearance
The true form of doppelgängers tends to basically look like humanoid blobs of green slime (basically think a combination of a human, a Polymorph from Ben 10, from Pokémon, and B.O.B, from Monsters vs. Aliens). They tend to have vaguely humanoid figures from the "waist" up, with a face and arms, hair, etc, made entirely out of slime, and everything from the "waist" down is basically like a big green B.O.B.-shaped blob.

Behavior
D oppelgängers tend to be rather skittish towards strangers, and tend to use their shapeshifting powers whenever they are surprised/frightened, however, once one gets to know a d oppelgänger, one finds that they are truly friendly, and are invaluable allies and friends for life.

Powers

 * Elasticity: D oppelgängers have the ability to stretch, deform, expand, or contract their bodies into any form imaginable.
 * Injury immunity:  D oppelgängers, as their bodies are made entirely out of green slime, basically cannot be injured, as anything that could injure them just phases through them.
 * Shapeshifting:  D oppelgängers are one of the few true shapeshifters in the world, being able to reshape and transform their bodies into anything imaginable.
 * Matter ingestion:  D oppelgängers are able to ingest and digest/absorb anything that they can fit their mouths around (which, suffice it to say, is anything), without any harm to them.
 * Goo generation:  D oppelgängers are able to generate any type of goo that they want/need, of any consistency/viscosity, whether sticky, slippery, etc.

Weakness

 * Shock/surprise:  D oppelgängers, when they are in another form, can be knocked out of that form if they are taken by surprise and/or hit with a surprise attack.
 * Extreme temperatures: D oppelgängers, due to their semi-solid physiology, are weak to extreme changes in temperatures. If the temperature change is gradual, they can still remain stable, however, if the temperature is too hot too quickly, they may completely liquify. Also, if the temperature is too cold too quickly, they may become solid, and therefore, shatterable.