Aang, Airbending Master

When Aang enters, airbend another target creature. (Exile it. While it's exiled, its owner may cast it for {2} rather than its mana cost.)
Whenever one or more creatures you control leave the battlefield without dying, you get an experience counter.
At the beginning of your upkeep, create a 1/1 white Ally creature token for each experience counter you have.

Umara Raptor

Flying
Whenever this creature or another Ally you control enters, you may put a +1/+1 counter on this creature.

Harabaz Druid

{T}: Add X mana of any one color, where X is the number of Allies you control.

Appa, Steadfast Guardian

Flash
Flying
When Appa enters, airbend any number of other target nonland permanents you control. (Exile them. While each one is exiled, its owner may cast it for {2} rather than its mana cost.)
Whenever you cast a spell from exile, create a 1/1 white Ally creature token.

Oran-Rief Survivalist

Whenever this creature or another Ally you control enters, you may put a +1/+1 counter on this creature.

Suki, Kyoshi Warrior

Suki's power is equal to the number of creatures you control.
Whenever Suki attacks, create a 1/1 white Ally creature token that's tapped and attacking.

Beastcaller Savant

Haste
{T}: Add one mana of any color. Spend this mana only to cast a creature spell.

Ondu Cleric

Whenever this creature or another Ally you control enters, you may gain life equal to the number of Allies you control.

Momo, Rambunctious Rascal

Flying (This creature can't be blocked except by creatures with flying or reach.)
When Momo enters, he deals 4 damage to target tapped creature an opponent controls.

Sokka, Lateral Strategist

Vigilance
Whenever Sokka and at least one other creature attack, draw a card.

Tajuru Archer

Whenever this creature or another Ally you control enters, you may have this creature deal damage to target creature with flying equal to the number of Allies you control.

Kabira Evangel

Whenever this creature or another Ally you control enters, you may choose a color. If you do, Allies you control gain protection from the chosen color until end of turn.

Katara, the Fearless

If a triggered ability of an Ally you control triggers, that ability triggers an additional time.

Sylvan Advocate

Vigilance
As long as you control six or more lands, this creature and land creatures you control get +2/+2.

Haru, Hidden Talent

Whenever another Ally you control enters, earthbend 1. (Target land you control becomes a 0/0 creature with haste that's still a land. Put a +1/+1 counter on it. When it dies or is exiled, return it to the battlefield tapped.)