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.
A magician develops a new way to make scrolls and can sell more powerful spells for cheap. Problem is, whether the magician is aware of it or not, the spell's power comes from spirits trapped by the magic that makes the scroll. Once used to power the scroll, the spirit is driven mad by the forces that have ripped through it's being, and often develops a homicidal thirst to destroy the one who tormented it. The spell the spirit was used for may have left some residual power in the spirit to give it more abilities than it ever used to have.