Elemental Mimicry
User is able to transform their body completely into fundamental elements, including air, earth, electricity, fire, light, shadow, water, etc. Users transformed form can be either anatomically identical to their normal form, aside of being made of element, in which case it contains all to organs and is somewhat vulnerable to attacks. Alternately user can transform into homogenous matter, without any part of their form being more important than the other.
That sounds interesting.