shapeshift

Probably a back formation from shapeshifter.

shapeshift (third-person singular simple present shapeshifts, present participle shapeshifting, simple past and past participle shapeshifted)

1. (fantasy, mythology, intransitive) to change one's shape or form (into another) through often magical means, normally applied only to living beings.
2. (figuratively, intransitive) to undergo a noticeable change (in character for example), to metamorphosize.

• phaseshift