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.
Carnival revelers wear masks and concealing clothes. (Wearing of masks in Venice was first documented in the late 1200s) It allows for the social classes to mix, easing social tensions.