Have

Seascape Aerialist

Whenever this creature or another Ally you control enters, you may have Ally creatures you control gain flying until end of turn.

Maybe

Appa, Loyal Sky Bison

Flying
Whenever Appa enters or attacks, choose one —
• Target creature you control gains flying until end of turn.
• Airbend another target nonland permanent you control. (Exile it. While it's exiled, its owner may cast it for {2} rather than its mana cost.)

Getting

Avatar's Wrath

Choose up to one target creature, then airbend all other creatures. (Exile them. While each one is exiled, its owner may cast it for {2} rather than its mana cost.)
Until your next turn, your opponents can't cast spells from anywhere other than their hand.
Exile Avatar's Wrath.

Island

Ty Lee, Chi Blocker

Flash
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
When Ty Lee enters, tap up to one target creature. It doesn't untap during its controller's untap step for as long as you control Ty Lee.

Hakoda, Selfless Commander

Vigilance
You may look at the top card of your library any time.
You may cast Ally spells from the top of your library.
Sacrifice Hakoda: Creatures you control get +0/+5 and gain indestructible until end of turn.

Earthbending Student

When this creature enters, earthbend 2. (Target land you control becomes a 0/0 creature with haste that's still a land. Put two +1/+1 counters on it. When it dies or is exiled, return it to the battlefield tapped.)
Land creatures you control have vigilance. (Attacking doesn't cause them to tap.)

Combat Research

Enchant creature
Enchanted creature has "Whenever this creature deals combat damage to a player, draw a card."
As long as enchanted creature is legendary, it gets +1/+1 and has ward {1}. (Whenever enchanted creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {1}.)

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.

Talisman of Curiosity

{T}: Add {C}.
{T}: Add {G} or {U}. This artifact deals 1 damage to you.

Beastmaster Ascension

Whenever a creature you control attacks, you may put a quest counter on this enchantment.
As long as this enchantment has seven or more quest counters on it, creatures you control get +5/+5.

Turntimber Ranger

Whenever this creature or another Ally you control enters, you may create a 2/2 green Wolf creature token. If you do, put a +1/+1 counter on this creature.

Hinterland Harbor

This land enters tapped unless you control a Forest or an Island.
{T}: Add {G} or {U}.

Ghostly Touch

Enchant creature
Enchanted creature has "Whenever this creature attacks, you may tap or untap target permanent."

Suki, Courageous Rescuer

Other creatures you control get +1/+0.
Whenever another permanent you control leaves the battlefield during your turn, create a 1/1 white Ally creature token. This ability triggers only once each turn.

Overwhelming Stampede

Until end of turn, creatures you control gain trample and get +X/+X, where X is the greatest power among creatures you control.

It'll Quench Ya!

Counter target spell unless its controller pays {2}.

Cryptolith Rite

Creatures you control have "{T}: Add one mana of any color."

Tale of Katara and Toph

Creatures you control have "Whenever this creature becomes tapped for the first time during each of your turns, put a +1/+1 counter on it."

Plains

Lantern Scout

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

Aang, the Last Airbender

Flying
When Aang enters, airbend up to one other target nonland permanent. (Exile it. While it's exiled, its owner may cast it for {2} rather than its mana cost.)
Whenever you cast a Lesson spell, Aang gains lifelink until end of turn.

South Pole Voyager

Whenever this creature or another Ally you control enters, you gain 1 life. If this is the second time this ability has resolved this turn, draw a card.

Talisman of Progress

{T}: Add {C}.
{T}: Add {W} or {U}. This artifact deals 1 damage to you.

Waterbending Lesson

Draw three cards. Then discard a card unless you waterbend {2}. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)

Waterbender Ascension

Whenever a creature you control deals combat damage to a player, put a quest counter on this enchantment. Then if it has four or more quest counters on it, draw a card.
Waterbend {4}: Target creature can't be blocked this turn. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)

Tajuru Beastmaster

Rally — Whenever this creature or another Ally you control enters, creatures you control get +1/+1 until end of turn.

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Jasmine Dragon Tea Shop

{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast an Ally spell or activate an ability of an Ally source.
{5}, {T}: Create a 1/1 white Ally creature token.

Secret Tunnel

This land can't be blocked.
{T}: Add {C}.
{4}, {T}: Two target creatures you control that share a creature type can't be blocked this turn.

Graypelt Hunter

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

Mirror Entity

Changeling (This card is every creature type.)
{X}: Until end of turn, creatures you control have base power and toughness X/X and gain all creature types.

Forecasting Fortune Teller

When this creature enters, create a Clue token. (It's an artifact with "{2}, Sacrifice this token: Draw a card.")

Oran-Rief Survivalist

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

Tocasia's Welcome

Whenever one or more creatures you control with mana value 3 or less enter, draw a card. This ability triggers only once each turn.

Kyoshi Warriors

When this creature enters, create a 1/1 white Ally creature token.

Descendants' Path

At the beginning of your upkeep, reveal the top card of your library. If it's a creature card that shares a creature type with a creature you control, you may cast it without paying its mana cost. If you don't cast it, put it on the bottom of your library.

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.

Kazandu Blademaster

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

Sol Ring

Forest

Momo, Playful Pet

Flying, vigilance
When Momo leaves the battlefield, choose one —
• Create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this token: You gain 3 life.")
• Put a +1/+1 counter on target creature you control.
• Scry 2.

Destined Confrontation

Each player chooses any number of creatures they control with total power 4 or less, then sacrifices all other creatures they control.

Sixth Sense

Enchant creature
Enchanted creature has "Whenever this creature deals combat damage to a player, you may draw a card."

United Front

Create X 1/1 white Ally creature tokens, then put a +1/+1 counter on each creature you control.

Unsettled Mariner

Changeling (This card is every creature type.)
Whenever you or a permanent you control becomes the target of a spell or ability an opponent controls, counter that spell or ability unless its controller pays {1}.

Aang, Destined Savior

Flying
Land creatures you control have vigilance.
At the beginning of combat on your turn, earthbend 2. (Target land you control becomes a 0/0 creature with haste that's still a land. Put two +1/+1 counters on it. When it dies or is exiled, return it to the battlefield tapped.)

Aang, at the Crossroads

Flying
When Aang enters, look at the top five cards of your library. You may put a creature card with mana value 4 or less from among them onto the battlefield. Put the rest on the bottom of your library in a random order.
When another creature you control leaves the battlefield, transform Aang at the beginning of the next upkeep.

Aang, at the Crossroads // Aang, Destined Savior

Titan of Littjara

As this creature enters, choose a creature type.
This creature is the chosen type in addition to its other types.
Whenever this creature enters or attacks, you may draw a card for each other creature you control that shares a creature type with it. If you do, discard a card.

Ondu Cleric

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

Tajuru Warcaller

Rally — Whenever this creature or another Ally you control enters, creatures you control get +2/+2 until end of turn.

Abandoned Air Temple

This land enters tapped unless you control a basic land.
{T}: Add {W}.
{3}{W}, {T}: Put a +1/+1 counter on each creature you control.

Hero of Goma Fada

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

Master Piandao

First strike
Whenever Master Piandao attacks, look at the top four cards of your library. You may reveal an Ally, Equipment, or Lesson card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Appa, Aang's Companion

Flying (This creature can't be blocked except by creatures with flying or reach.)
Whenever Appa attacks, another target attacking creature without flying gains flying until end of turn.

Yavimaya Coast

{T}: Add {C}.
{T}: Add {G} or {U}. This land deals 1 damage to you.

Cathars' Crusade

Whenever a creature you control enters, put a +1/+1 counter on each creature you control.

Don't Have

Avatar Enthusiasts

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

Team Avatar

Whenever a creature you control attacks alone, it gets +X/+X until end of turn, where X is the number of creatures you control.
{2}{W}, Discard this card: It deals damage equal to the number of creatures you control to target creature.

The Mechanist, Aerial Artisan

Whenever you cast a noncreature spell, create a Clue token. (It's an artifact with "{2}, Sacrifice this token: Draw a card.")
{T}: Until end of turn, target artifact token you control becomes a 3/1 Construct artifact creature with flying.

Waterbender's Restoration

As an additional cost to cast this spell, waterbend {X}. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)
Exile X target creatures you control. Return those cards to the battlefield under their owner's control at the beginning of the next end step.

Exotic Orchard

{T}: Add one mana of any color that a land an opponent controls could produce.

Invasion Reinforcements

Flash
When this creature enters, create a 1/1 white Ally creature token.

The Earth King

When The Earth King enters, create a 4/4 green Bear creature token.
Whenever one or more creatures you control with power 4 or greater attack, search your library for up to that many basic land cards, put them onto the battlefield tapped, then shuffle.

Negate

Herald's Horn

As this artifact enters, choose a creature type.
Creature spells you cast of the chosen type cost {1} less to cast.
At the beginning of your upkeep, look at the top card of your library. If it's a creature card of the chosen type, you may reveal it and put it into your hand.

Elven Chorus

You may look at the top card of your library any time.
You may cast creature spells from the top of your library.
Creatures you control have "{T}: Add one mana of any color."

Herd Heirloom

{T}: Add one mana of any color. Spend this mana only to cast a creature spell.
{T}: Until end of turn, target creature you control with power 4 or greater gains trample and "Whenever this creature deals combat damage to a player, draw a card."

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.

Metallic Mimic

As this creature enters, choose a creature type.
This creature is the chosen type in addition to its other types.
Each other creature you control of the chosen type enters with an additional +1/+1 counter on it.

Nature's Claim

Destroy target artifact or enchantment. Its controller gains 4 life.

Harabaz Druid

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

Earth Kingdom General

When this creature enters, earthbend 2. (Target land you control becomes a 0/0 creature with haste that's still a land. Put two +1/+1 counters on it. When it dies or is exiled, return it to the battlefield tapped.)
Whenever you put one or more +1/+1 counters on a creature, you may gain that much life. Do this only once each turn.

Sokka's Charge

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

Umara Raptor

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

Aang and La, Ocean's Fury

Reach, trample
Whenever Aang and La attack, put a +1/+1 counter on each tapped creature you control.

Aang, Swift Savior

Flash
Flying
When Aang enters, airbend up to one other target creature or spell. (Exile it. While it's exiled, its owner may cast it for {2} rather than its mana cost.)
Waterbend {8}: Transform Aang.

Aang, Swift Savior // Aang and La, Ocean's Fury

White Lotus Reinforcements

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

White Lotus Tile

This artifact enters tapped.
{T}: Add X mana of any one color, where X is the greatest number of creatures you control that have a creature type in common.

Hada Freeblade

Cloudshift

Exile target creature you control, then return that card to the battlefield under your control.

Panharmonicon

If an artifact or creature entering causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.

Blade of Selves

Equipped creature has myriad. (Whenever it attacks, for each opponent other than defending player, you may create a token copy that's tapped and attacking that player or a planeswalker they control. Exile the tokens at end of combat.)
Equip {4}

Path of Ancestry

This land enters tapped.
{T}: Add one mana of any color in your commander's color identity. When that mana is spent to cast a creature spell that shares a creature type with your commander, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

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.

Secluded Courtyard

As this land enters, choose a creature type.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a creature spell of the chosen type or activate an ability of a creature source of the chosen type.

Earth Kingdom Jailer

When this creature enters, exile up to one target artifact, creature, or enchantment an opponent controls with mana value 3 or greater until this creature leaves the battlefield.

Honest Work

Enchant creature an opponent controls
When this Aura enters, tap enchanted creature and remove all counters from it.
Enchanted creature loses all abilities and is a Citizen with base power and toughness 1/1 and "{T}: Add {C}" named Humble Merchant. (It loses all other creature types and names.)

Earth King's Lieutenant

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

Enduring Innocence

Lifelink
Whenever one or more other creatures you control with power 2 or less enter, draw a card. This ability triggers only once each turn.
When Enduring Innocence dies, if it was a creature, return it to the battlefield under its owner's control. It's an enchantment. (It's not a creature.)

Brushland

{T}: Add {C}.
{T}: Add {G} or {W}. This land deals 1 damage to you.

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.

Chart a Course

Draw two cards. Then discard a card unless you attacked this turn.

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

An Offer You Can't Refuse

Counter target noncreature spell. Its controller creates two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

Origin of Metalbending

Choose one —
• Destroy target artifact or enchantment.
• Put a +1/+1 counter on target creature you control. It gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)

Jet, Rebel Leader

Whenever Jet attacks, look at the top five cards of your library. You may put a creature card with mana value 3 or less from among them onto the battlefield tapped and attacking. Put the rest on the bottom of your library in a random order.

Golden Ratio

Draw a card for each different power among creatures you control.

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.)

Legion Loyalty

Creatures you control have myriad. (Whenever a creature with myriad attacks, for each opponent other than defending player, you may create a token copy that's tapped and attacking that player or a planeswalker they control. Exile the tokens at end of combat.)

Adarkar Wastes

{T}: Add {C}.
{T}: Add {W} or {U}. This land deals 1 damage to you.