I love things to be symmetrical. The correlations between the elements may not be symmetrical, but they do have certain similarities.
In this graphic , every element has got one certain "life hack" - the small circle on the counterclockwise-side of the big outer circles. On the clockwise-side there are subskills; and the big circles should demonstrate kind of an ultimate bending style. Furthermore, I crossed the bordering elements, and in the centre is, of course, Energybending.
The Life-Hacks: These techniques are skills which help the bender survive certain surroundings or to withstand situations, just as you want. People would say these aren't really "skills" because they aren't used so actively. But I see them as bending just like a fighting technique.
The Subskills: I struggled with making a clear difference between them and the ultimates. But the main thing of them is that you bend the origin element in a way which is kind of lost in the ultimates.I would even say, with these skills you bend an "enhanced mode" of the element itself.
The Ultimates: They have a greater distance to the origin. They are not just enhanced, they are really a different thing to bend. In the case of earth and fire, they are even a completely different art of bending, as you don't bend air whilst levitating, but you "detach yourself from earthen matters" like it is described, so you master the "heart" of bending, in that case freedom itself.
The Crossings: You can't really cross elements so that benders of two nations can bend it. When an earthbender bends mud, he doesn't actually bend the wet earth, the earth mixed with water, but the bare earth and I'm sure if you "hold" it a while, it would/should dry out. The same with water, but the other way round.
The major deficits are:
- Energy reading: What makes this skill difficult is that it was only shown once, and in addition, in a rather short scene. We even don't really know what the bender was doing there, we can only assume. Instead of Energy Reading I would prefer a skill that refers to the possibility of manipulating electricity with firebending.
- Heat: Frankly, this was the last part for me to add to the graph and I just did it that I even had a thing so I could upload the graph and ask others for their opinion. I still don't know what could fit here.
- Vacuum: I took this because I thought it would be quite difficult to hold a vacuum due to the negative pressures. But I'm not an expert in physics so I don't know if it's really so difficult. However, there may be things one can do with a vacuum we don't know. Who knows?
- Lava: I know that a firebender can't bend lava as it's just melted earth. Is there a better choice?