I live in a rural, forest area. We have all manner of wildlife here that's dangerous when you mess with them.
However, most animals aren't really aggressive. Sure, they'll attack if cornered, or if they're hurt or rabid, but generally speaking, they'd prefer to avoid humans. Still, if encountered in the appropriate circumstances, there's wolves and coyotes and snakes and bears and insects and even deer and raccoons can be dangerous.
Now, if you want aggressive dangerous animals...
Bears aren't generally aggressive, at least, not the bears we have here. UNLESS they're mother bears protecting cubs, in which case, they will destroy you. Or if they've become acclimatized to humans. Nearly all the bear attacks that have happened in this area have been due to humans getting to close to baby and getting mauled, or bears associating humans with food through ill-advised feeding and dumpsters. They WILL not hesitate to eat you if you don't give them the food they think you have.
Wild boars are just mean. Stupidly mean. Someone above said they were about 250 lbs, but the ones we have here are bigger than that. They're bigger than the bears. I have seen a wild boar leave dents in the bars of a cage made of inch thick steel stock. I have no idea why they're so aggressive, but they don't need a reason to try to murder you.
Something you might not have thought of, but are likely to have closer to towns or former towns are feral dogs. We had a pack of those here a few years ago; escaped from people's property or just abandoned. (In this area, dogs aren't usually leashed or penned.) They're not afraid of people, like the acclimatized bears. They can be worse, though, because while they're individually smaller, they form packs. Think of them like wolf packs that don't avoid people.
And if your party ventures anywhere near a lake or a river, swans, geese, and snapping turtles are all surprisingly awful. Swans and geese WILL attack aggressively, especially during nesting season. And snapping turtles, in addition to being ill-tempered, can bite through fingers and other extremities.
Also, badgers. Forgot about badgers and their ilk. Like wolverines.