[quote=@Bluetommy]In terms of lavabending being equally possible in both the firebending and earthbending disciplines, there is precedent from the show, two of the known lavabenders are Kiyoshi, an earthbender, and Roku, a firebender. It makes complete sense to me that these disciplines are connected in such a manner.[/quote]
LoK actually jossed that, IIRC - by canon lavabending is a specialised Earth technique. Which is stupid.

[quote=Bluetommy]In terms of cross-bending abilities, study of the other bending arts has been shown to lead to greater abilities in the show, Iroh creating lightning redirection through studying waterbenders being the most obvious of these. In terms of the examples you gave, I don't think it makes sense for airbenders to be able to stormbend simply by watching waterbenders, unless the storm already exists it makes little sense to me for Airbenders to suddenly gain the ability to create storms, mud has been bent by both water and earthbenders without any interaction between the two, and heat manipulation is an intermediate level firebending technique, Iroh uses it to heat tea, Zuko uses it to melt ice, Sozin uses it to attempt to halt a volcanic eruption. None of these people outside Iroh had had the chance to study airbenders prior to use.'[/quote]
So, in order - airbenders certainly couldn't stormbend just by watching waterbenders; I see Stormbending as a Master-Level technique (which means Inner Gale and one Airbending Style at Mastery) also requiring Mastery in Study of Water and Study of Fire. That's like, endgame stuff. And doing anything big with it would probably completely wipe you out even [i]then[/i], plus falling into Dangerous Forbidden Move classification, because if you let a storm get out of your control and it [i]grows[/i]? Hurricanes are [i]Avatar[/i] territory.

You are more or less correct about mud, I threw that in mostly offhand; that would probably be Novice level in Study of Water/Earth for earth/waterbenders, respectively, since mud is stiffer than water but more fluid than earth. You could get that just by carefully watching the appropriate type of bender do their thing for a while, but if you want to start getting deeper into Study of [Element] you need to actually learn the forms and what they do, and then start experimenting with how you incorporate some of those things into your own style. Master-level Study of Water means [i]mastering Master-level waterbending forms and then picking out the bits that are applicable to your own element.[/i]

Heatbending, as I visualise it, is not quite the same thing as heat manipulation - heating tea and melting ice, the way I've been thinking of them, fall under the 'can radiate warmth' part of Inner Flame, the most basic Universal-level firebender skill; what Sozin does with the volcano is Novice or [i]maybe[/i] Apprentice level heatbending, just moving it from one place to another. Combat heatbending, though, I see as stuff like throwing around blasts of superheated air, more or less instantly dropping the space around someone to minus fifty and then dumping that all onto the guy standing next to him: just as dangerous as most sorts of firebending, and a whole lot less visible.

If you look at the Avatar wiki, there's a line about heat manipulation, referring specifically to Sozin's heat redirection: [i]It appears to operate on a similar principle to Iroh's redirection of lightning technique.[/i] Hence, if Study of Water leads to lightning manipulation, Study of Air leads to heat manipulation - and if lightning redirection graduates into proper, controlled lightningbending, logically speaking, heat redirection should graduate into heatbending.

[quote=Bluetommy]Hmm, this is all quite interesting, I see no reason to say no. In terms of defensive firebending, be sure to recall that for a long time those arts were forgotten, and even if my setting is earlier in the timeline, the warlike state of the Fire Islands and aggressive focus of the most powerful warlord may lead to it being far rarer than the aggressive form.

If this structure will help you, I won't stop you, though this is a casual RP and I won't expect the same from everyone else.

Also another piece of setting information that I may have forgotten to mention, as this RP is far earlier in the timeline, the spirit world will be more closely linked with the physical.[/quote]
Well, it's not [i]purely[/i] defensive, it's just more focused on control and the flow of fire rather than aggression and power; that results in better deflection. It doesn't, in and of itself, give you anything special, or at least not until you hit Mastery and unlock [b]Cloak of Flame[/b], the defensive counterpart to Mountain's [b]Endless Onslaught[/b]. Rather, if Mountain Style is a straight line, Dragon Style is an arc or a circle; you can stab things better with a line, but moving in an arc is better for deflection. Both Mountain and Dragon defend by knocking things away or just incinerating them with fire; Dragon is simply better at it than Mountain, as Mountain is better on the offence than Dragon.

And the reason my firebender knows Dragon style, and is in fact better at it than Mountain, is that he learned from a dragon (this being centuries before Sozin wiped them out, they're probably a lot more common.) He's peasant-born, so his parents couldn't teach him, and none of his family are very fond of [i]any[/i] of the warlords - that's part of why he's searching for the Avatar, in fact, because he's hoping the Avatar will lay down the law on them.

[quote=@Demon Shinobi]WOAH DUDE!
This is a little complication, but like really cool. 
I might be like... Behind on info, but is that stuff all legit canon names for things or did you make some of it up? I kind wanted a fire bender, but now idk if I could compete lol Still really cool though
[/quote]
Oh, I know it's complicated. I just enjoy that sort of thing.

Most of those names aren't canon; Lavabending and Lightningbending [i]are[/i], and we know that Iroh studied waterbending to come up with his lightning redirection technique, as well as the fact that he could breathe fire without external motions. So Study of Water/Earth/Air is a formalised name for doing that sort of thing that I came up with, and Inner Flame and Surging Breath describes the firebender ability to manipulate both flame and chi by breathing, but most of the other stuff isn't canon.

Cross-element bending abilities I drew primarily from [i]Embers[/i], in which - among other things - Zuko invents hot water bending in order to disguise himself on the run, then later, working with Toph, molten glass bending (which they can both do) while she also learns to bend ashes in the air above an open flame. So I took that and went along the logical progression. 

Chi use by warriors is also, I think, from [i]Embers[/i] (Sokka learns it) - we get [i]hints[/i] of that being the case in canon, both because Piandao is simply too awesome [i]not[/i] to be doing [i]something[/i] wacky and because chi-blocking causes paralysis rather than just stopping bending. That is, if no chi means you can't move, more chi should mean you can move [i]more[/i] or [i]more powerfully[/i]. I say [i]I think[/i] because I don't know if it ever actually became an acknowledged [i]thing[/i] in canon or just fell under 'this is a fantasy world, there are people who can take on a hundred men using only a sword and come out without a scratch.'