here could be Giant Aether Falcons, which you find in valkyrie places and are the valkyrie steeds that they ride, and if you get close enough to them a bar appears above their heads with red on the left side, black the far rleft, green on the right side, gold on the far right, and below that it says neutral until you interact with them, and by being mean to them, like hurting them, the bar left. In red the neutral becomes angry, in black it becomes hostile. By being kind, like feeding them, the bar goes right, in green It is friendly and in gold it is tame, when tame you can ride it with saddle, and when hostile they try to kill you, in friendly they follow you, and angry they peck at you till at at seven hearts. If you kill one you get falcon feather saga and or falcon beak. With the feathers you can make falcon wings, and with the beak you make falcon arm or. But if one of them goes hostile all the others in a fifty block radius go angry. The tame ones can fly with you on them.
These should also be an option to be a demon (nether), human (over world), or angel (aether). You spawn in the corresponding race for each world. Angels get strength 2 in the over world because of extra oxygen, demons get weakness 2 because of less heat, humans get nothing. Humans get strength 2 in the aether because of heavenly light, demons get strength 2 because of e deadlines danger is absorbed by their evil, and angels get nothing. Demons get nothing in the nether, humans get weakness 2 because it is the land of the dead and evil, and angels get weakness 2 because the same reason.