These are probably never going to be seen at all, but it’s fun to think about.
Nature-Bending, subsidiary of Earth-bending, nature, plants, and flowers manipulation.
This would be somewhat cool as a cameo for a young Earth-Bender to be able to do it. They could rap extremely strong vines around their opponents and trap their opponents in Venus-fly traps. However most of the people would just break out of the vines.
Plasma-bending, plasmas and molecules manipulation, a subsidiary of water-bending.
Being able to do this would be so overpowered and kind of cool. Although to keep this from be coming too overpowered in a sense of the show, it’ll be very unstable and can backfire easily.
Sound-bending, a subsidiary of Earth and Water bending, sound wave manipulation.
This is probably the one that makes the least sense, but we’re gonna roll with it. Sound bending is the manipulation of sound waves Earth and Water. Earthbenders could use this to cause Earthquakes and Water benders can use this to make waves to crash into their enemies.
Storm-bending, a subsidiary of Air-bending, Storm manipulation,
Airbenders could use this to summon storms using the power of anger. This has already seen a bit when it comes to Aang, but it would be more envolved with the weather.
These are just some okay ideas of bending. They are probably bad, and I will probably get hated for some of these.