Normal Animals. Monsters are not exceptional without regular animals to compare them to. In most roleplaying games, animals are simply window-dressing. If statistics are needed for something simple like a cow or a dog, it is enough to use the rules for minions. Larger and more dangerous animals have their own statistics. 

 

Legendary Animals. Much like humanoids, animals grow in power with age and experience. If you need a convenient excuse for why this happens, their greater prowess can be attributed to the subtle influence of nature spirits. This is important because it allows for the creation of fearsome predators, or animal companions that remain relevant in mid to high-level play. 

 

Dire Beasts. Giant animals are a staple of fantasy settings. They are normally created by supernatural phenomena, fey influence, or the blessings of animal spirits. Much like Chymerics, they can spontaneously appear in any wild setting within a matter of weeks. Giant reptiles, insects, and arachnids also fall under this category. 

Alien Fauna. In some settings, animals exist with no direct analog in the current world. To be categorized as a beast, a creature must fit into the natural ecosystem and not have any magical powers or traits. This is particularly important for druids, who can only wildshape into beast forms they have studied firsthand. Dinosaurs, Tyrgs, Axebeaks, Minotaur Lizards, and other creatures are all technically beasts, despite their deadliness.