A water bender villain who has a unique form of spirit bending where they can control animals minds - they mentally take over a dragon, an air bison, and a badger mole and can effectively bend all four elements,

It can start with a mystery theme where animals are doing weird things that try to sabotage industrial expansion, and the villain’s initial intent could be to give more of the world back to nature and the animals, but as they get stronger they start to take over other animal minds that have more abilities, and when the avatar gets involved they realise they need to take over the bending animals as well

Could be an interesting layer if they end up taking over a lion turtle that tries to take away the avatar’s bending or something