Nestled between the towering cliffs of the Zorian plateau, lies a vast cavity that is wide enough to swallow an adult bull elephant with enough space to spare for a small herd of draft horses on either side. There you will find gold, an abundance of it. But what is that you say? That the natives tell you that it is a place of death and home to hideous monster that will devour you? Ignore the savages. They only seek to protect what they are too indolent to grab for themselves.
-A Khanate offical assuring a bunch of miners.
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.