Halimar Excavator

Whenever this creature or another Ally you control enters, target player mills X cards, where X is the number of Allies you control.

Morophon, the Boundless

Changeling (This card is every creature type.)
As Morophon enters, choose a creature type.
Spells of the chosen type you cast cost {W}{U}{B}{R}{G} less to cast. This effect reduces only the amount of colored mana you pay.
Other creatures you control of the chosen type get +1/+1.

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.

Katara, the Fearless

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

Aligned Heart

Flurry — Whenever you cast your second spell each turn, put a rally counter on this enchantment. Then create a 1/1 white Monk creature token with prowess for each rally counter on it. (Whenever you cast a noncreature spell, the token gets +1/+1 until end of turn.)

Aang and Katara

Whenever Aang and Katara enter or attack, create X 1/1 white Ally creature tokens, where X is the number of tapped artifacts and/or creatures you control.

White Lotus Reinforcements

Vigilance
Other Allies you control get +1/+1.

Allied Reinforcements

Create two 2/2 white Knight Ally creature tokens.

Akoum Battlesinger

Haste
Whenever this creature or another Ally you control enters, you may have Ally creatures you control get +1/+0 until end of turn.

Firemantle Mage

Rally — Whenever this creature or another Ally you control enters, creatures you control gain menace until end of turn. (A creature with menace can't be blocked except by two or more creatures.)

Earthen Ally

This creature gets +1/+0 for each color among Allies you control.
{2}{W}{U}{B}{R}{G}: Earthbend 5. (Target land you control becomes a 0/0 creature with haste that's still a land. Put five +1/+1 counters on it. When it dies or is exiled, return it to the battlefield tapped.)

Boiling Rock Rioter

Firebending 1 (Whenever this creature attacks, add {R}. This mana lasts until end of combat.)
Tap an untapped Ally you control: Exile target card from a graveyard.
Whenever this creature attacks, you may cast an Ally spell from among cards you own exiled with this creature.

Tuktuk Scrapper

Whenever this creature or another Ally you control enters, you may destroy target artifact. If that artifact is put into a graveyard this way, this creature deals damage to that artifact's controller equal to the number of Allies you control.

Talus Paladin

Whenever this creature or another Ally you control enters, you may have Allies you control gain lifelink until end of turn, and you may put a +1/+1 counter on this creature.

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.

Hagra Diabolist

Whenever this creature or another Ally you control enters, you may have target player lose life equal to the number of Allies you control.

Allied Teamwork

When this enchantment enters, create a 1/1 white Ally creature token.
Allies you control get +1/+1.

Ondu Cleric

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

Mai and Zuko

Firebending 3
You may cast Ally spells and artifact spells as though they had flash.

Murasa Pyromancer

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

Harabaz Druid

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

Allies at Last

Affinity for Allies (This spell costs {1} less to cast for each Ally you control.)
Up to two target creatures you control each deal damage equal to their power to target creature an opponent controls.

Vastwood Animist

{T}: Target land you control becomes an X/X Elemental creature until end of turn, where X is the number of Allies you control. It's still a land.

Sokka's Charge

During your turn, Allies you control have double strike and lifelink.

Chasm Guide

Rally — Whenever this creature or another Ally you control enters, creatures you control gain haste until end of turn.

Avatar Enthusiasts

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

Invasion Tactics

When this enchantment enters, creatures you control get +2/+2 until end of turn.
Whenever one or more Allies you control deal combat damage to a player, draw a card.

Agadeem Occultist

{T}: Put target creature card from an opponent's graveyard onto the battlefield under your control if its mana value is less than or equal to the number of Allies you control.

Ally Encampment

{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast an Ally spell.
{1}, {T}, Sacrifice this land: Return target Ally you control to its owner's hand.

Angelic Captain

Flying
Whenever this creature attacks, it gets +1/+1 until end of turn for each other attacking Ally.

Sokka, Tenacious Tactician

Menace, prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Other Allies you control have menace and prowess.
Whenever you cast a noncreature spell, create a 1/1 white Ally creature token.