Changeling

Changeling is generally used in fiction for a shapeshifting entity. Known alien races called Changelings include but are not limited to:
 * Changeling - also known as an Icejin or Frieza's Race - are the conjectural names given by fans for over a decade to Frieza's species in Dragon Ball, which shifts forms to hide behind "proxy" power levels.
 * Changeling, the name of Odo's amorphous blob species in Star Trek.