Shapeshifting/Analysis

Required Secondary Powers
Characters that shift into other objects also have the ability to ignore how said objects would ordinarily hurt people. For example, someone who could become living flame is also immune to being burned (either by their own flame or that of others). Someone who can turn into water often gains the ability to breathe in water (or has no need to breathe at all).

Most shape shifters would need an eidetic memory to convincingly imitate every detail of a person they've seen once. Or an encyclopedic knowledge to remember the details of a multitude of objects. This is more commonly averted, as they are just as frequently exposed as fakes because of such a flaw in the disguise, or they are copying someone they are fairly familiar with, or they are even not copying anyone and just using their imagination.

There's also the issues of surviving while transforming and in the transformed state (altering one's body structure even a little is usually fatal in the real world, let alone having your flesh turned into another substance or turning into something with no internal organs) and keeping the ability to shape shift rather than transforming into something cursed with permanent Shapeshifter Mode Lock... This one could fill a page on its own.

There's also the question of how a shape shifter thinks with no brain, or just without their normal brain.

And of course, if the shape shifter can also change his mass...