In a nearby town villagers tell tales of adventurers being driven mad by an unknown force within the woods…
When a local farmer discovers something at the bottom of his new well, the fate of the land will hang in the balance.
During their travels through a dense wooded area the high pitched sound of a scream tears through the peacefulness of the forest.
This mountain chain was once vast and impenetrable, but had the misfortune to named in the binding spell of a mighty demonic(godly?) being, namely that when the Great Mountains are forgotten, then shall it be free.
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.