with the addition of bees in the newest 1.15 snapshot, i think bears would be a great addition to the game. They would spawn naturally in dark oak forest biomes, and are passive-aggresive (similar to wolves). The bears can be lured and bred using honey combs (just introduced in the snapshot), and can often be found eating bee-nests in the wild. The bees will not be able to harm the bear. There is also a small chance that you will find a bear hibernating close to the entrance to a cave near a dark oak forest. So what do you think?