In the middle of an unimportant combat with some bandits a burst of wild magic transforms all of the PCs and their opponents in to random animals and monsters. They retain their intelligence (though not, of course, the ability of speech). They can either carry on the combat in their new forms, panic, or otherwise react how they see best. After about an hour, they return, unharmed, to their normal form.
The Black Forest- actually a part of another forest, is said to be cursed by the presence of some horrific monster, which burns the very earth with its body!
No one has yet seen it and lived to tell, so be warned!(see NPC Aurelius Blackfoot for details)