Second AbaddonSK's comment. Ether Saga's Chinese name is Pocket Xiyou - reminds you of Pokemon, doesn't it? Actually ESO does have the exact same idea - you can virtually catch and tame any mob you encounter, equip your pet with bells to strengthen its attributes, and like any other pet it can battle for / along side you, you can even fuse with your pet and add your attributes together! Combine two pets into a much more powerful one. There's also special flying pets or mount ones.
Sometimes mobs drop morph cards and you can morph into that mob - in the case of flying mobs you can morph into the mob and pvp in air! I've basically skimmed the surface, for more info see Ether Saga OL's official site here
, good luck playing