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.
Inspired by Ria Hawk's winged mushroom picture:
The winged mushrooms (Lerreta Meia) are a species of giant insect indigenous to the leafy areas of Udnalor, Kingdom of the Gnomes. Outwardly they appear much the same as ordinary giant mushrooms, and they graze in the bulbous fungal glades. However, this is merely an elaborate camouflage: the insect beneath is a fungivore and prone to fly off when it encounters another creature. Sometimes gnome farmers mistake them for crop mushrooms. They're in for a surprise when they do.