If a creature is transformed into another creature (say, a human into a dog), then that creature will become more and more accustomed to the new form until a point is reached where reversing the spell is impossible. A second transformation is possible, but the creature will have to go through the whole process again.
An ancient, psuedo-immortal race has been manipulating something important (politics, religion, economics, etc.) for centuries. Hardly anyone is aware of them, let alone their goals.
A noble claims that a stranger did not enter the town by any normal means, but trough his mirror. The man in question is ravening mad and mutters on about vast halls connecting all the mirrors in the world.