I was thinking about this a while ago, and I wrote a few pages of notes while I was working on the subject.
Here are some of the things I cam up with.
SEPARATE CLASSES?
Yes.
While some powers could definitely cross over, I think that different bending styles are probably functionally different enough to warrant different classes. This is mainly because I would like to see the different bending styles have different class abilities.
While there are some powers that could overlap in functionality, this could be executed by having several generic powers available to each of the classes. I would personally shy away from this, as I would love to see each bending style as being functionally different.
PRIME STATS
I worked out the prime stats for each class using two methods:
a) What stats suit the class
b) Looking at the opposite bending style, and not having overlapping stats between the two.
This is what I ended up with:
Fire – Charisma, Dexterity & Strength
Water – Wisdom, Intelligence & Constitution
Earth – Wisdom, Constitution & Strength
Air – Intelligence, Charisma & Dexterity
(Although perhaps Earth and air should swap wisdom and intelligence as their primary stat, due to Air’s nomadic nature, and earth’s propensity to build vast nations and cities, and utilize structured battlefield tactics. what do you guys think?)
ROLES
I spent a while thinking about this one, and came up with a fundamental question – Why couldn’t an air bender be a striker, a controller or even a defender or a leader, if that’s what they’ve trained to do? Certainly, there are instances of striker-like earth benders, and controller-like fire benders. Conceptually, there’s no reason that they couldn’t exist.
But how to make it work? The solution I came up with went something like this:
Rather than creating a separate class for each option, use a structure somewhat similar to the warlock pacts. In addition to choosing a bending style, you pick a role, which decides one (or more) of your class abilities, and offers a bonus to certain powers, much like some warlock powers, but with modifications relating to role. (I believe someone did something similar to this when they where creating a 4e superhero system, but I don’t have the link to that anymore…)
SAMPLE CLASS ABILITY
Ignite Passions.
Using the ignite passions power, a Fire-bending leader is able to get the best out of his troops… by kindling their rage and fury, allowing them to throw themselves into the fray with renewed vigor.
Ignite Passions Fire Leader Feature
You kindle a spark of energy within the target’s soul, spurring them on to acts of heroism… or villainy.
Encounter (Special) Elemental[fire], Healing
Special: You can use this power twice per encounter, but only
once per round. At 16th level, you can use this power three
times per encounter.
Minor Action Close burst 5
(10 at 11th level, 15 at 21st level)
Target: You or one ally
Effect: The target can spend a healing surge and deals an additional d6 damage on their next attack.
Increase the amount of additional damage dealt to 2d6
at 6th level, 3d6 at 11th level, 4d6 at 16th level, 5d6 at
21st level, and 6d6 at 26th level.
POSSIBLE OPTION: Roles and Primary Stats.
If you wanted, it would be possible to have different roles within a bending style focusing on different primary and secondary stats. This would ensure that the characters feel different, and that their role reflected their personality.
It would look something like this:
Fire: Leader: Charisma/Dexterity
Controller: Dexterity/Charisma
Striker: Dexterity/Strength
Defender: Strength/Charisma.
Water: Leader: Wisdom/intelligence
Controller: Constitution/Intelligence
Striker, Intelligence/Constitution
Defender: Constitution/Wisdom.
Earth: Leader: Wisdom/Constitution
Controller: Wisdom/Strength
Striker: Strength/Wisdom
Defender: Constitution/Strength.
Air: Leader: Intelligence/Dexterity
Controller: Charisma/Dexterity
Striker: Dexterity/Charisma
Defender: Intelligence/Dexterity
It might be a little clunky to implement, but it would provide nice variations within the bending styles.
MULTICLASSING
Just a few random thoughts:
No multiclassing into other bending classes.
It could be possible to ‘multiclass’ into another role of your bending style.
THE AVATAR
The Avatar should probably function as a complete character arc, with heroic-tier multiclass-like feats, a paragon path and an epic destiny. I would be quite fun to make.
I’ve got some more notes, but that’s probably plenty for now

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