There is a corporeal being that can radically change its shape to such an extent that it seems to become something entirely different.

Notes:
This theme applies only if the ability is, more or less, intrinsic to the being's species. I.e., it does not apply if technology is used. Nor does it typically apply to "transcendental beings" (beings who are so advanced that their capabilities seem like magic to us), or incorporeal beings, unless an innate shapeshifting ability is explicitly explained as such.

References:
https://en.wikipedia.org/wiki/Shapeshifting http://www.sf-encyclopedia.com/entry/shapeshifters