[Thorhammer]

Originally Posted by Fat Swagodile

Let's say you have Gengar in your second slot. When Zoroark is sent out, it will take the form of Gengar. Now let's say you send out the real Gengar later on, and switch with, let's say, Toxicroak. Toxicroak is now in the second slot, meaning that next time Zoroark comes out, it will take the form of Toxicroak instead of Gengar.

Basically, you'll never know whether you're fighting Zoroark or the real deal, since Zoroark also copies the name of the Pokemon it's impersonating.

But not the HP.

At least, I assume.