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.
Magical forests are never a good place to sleep, especially seeing as much of the population is nocturnal. Firewood taken from the wrong tree can turn against its collectors, and a strangling onslaught of angry twigs and branches can be surprisingly severe and difficult to disentangle yourself from. Fires themselves attract enemies, and not only malevolent predators. Giant moths and gloomwings are tempted by the heat and light, but are often misunderstood.