Have

Combustion Technique

Combustion Technique deals damage equal to 2 plus the number of Lesson cards in your graveyard to target creature. If that creature would die this turn, exile it instead.

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

Enter the Avatar State

Until end of turn, target creature you control becomes an Avatar in addition to its other types and gains flying, first strike, lifelink, and hexproof. (A creature with hexproof can't be the target of spells or abilities your opponents control.)

Sun Warriors

Firebending X, where X is the number of creatures you control. (Whenever this creature attacks, add X {R}. This mana lasts until end of combat.)
{5}: Create a 1/1 white Ally creature token.

Putting in

Appa, the Vigilant

Flying, vigilance
Whenever Appa or another Ally you control enters, creatures you control get +1/+1 and gain flying and vigilance until end of turn.

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.

Proxy

Talisman of Progress

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

Airbending Lesson

Airbend target nonland permanent. (Exile it. While it's exiled, its owner may cast it for {2} rather than its mana cost.)
Draw a card.

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.)

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.

Captain's Claws

Equipped creature gets +1/+0.
Whenever equipped creature attacks, create a 1/1 white Kor Ally creature token that's tapped and attacking.
Equip {1}

Sokka's Sword Training

Target creature gets +2/+2 until end of turn.
Create a Clue token. (It's an artifact with "{2}, Sacrifice this token: Draw a card.")

Fellwar Stone

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

Gran-Gran

Whenever Gran-Gran becomes tapped, draw a card, then discard a card.
Noncreature spells you cast cost {1} less to cast as long as there are three or more Lesson cards in your graveyard.

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.

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.

Sokka's Charge

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

How to Start a Riot

Target creature gains menace until end of turn. (It can't be blocked except by two or more creatures.)
Creatures target player controls get +2/+0 until end of turn.

Firebending Lesson

Kicker {4} (You may pay an additional {4} as you cast this spell.)
Firebending Lesson deals 2 damage to target creature. If this spell was kicked, it deals 5 damage to that creature instead.

Katara, Bending Prodigy

At the beginning of your end step, if Katara is tapped, put a +1/+1 counter on her.
Waterbend {6}: Draw a card. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)

Anointed Procession

If an effect would create one or more tokens under your control, it creates twice that many of those tokens instead.

Prairie Stream

({T}: Add {W} or {U}.)
This land enters tapped unless you control two or more basic lands.

Princess Yue

When Princess Yue dies, if she was a nonland creature, return this card to the battlefield tapped under your control. She's a land named Moon. She gains "{T}: Add {C}." (She's still legendary.)
{T}: Scry 2.

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.

Swords to Plowshares

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

Battlefield Forge

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

United Front

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

Training Center

This land enters tapped unless you have two or more opponents.
{T}: Add {U} or {R}.

Jeong Jeong, the Deserter

Firebending 1 (Whenever this creature attacks, add {R}. This mana lasts until end of combat.)
Exhaust — {3}: Put a +1/+1 counter on Jeong Jeong. When you next cast a Lesson spell this turn, copy it and you may choose new targets for the copy. (Activate each exhaust ability only once.)

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.

Reliquary Tower

You have no maximum hand size.
{T}: Add {C}.

Fancy Footwork

Untap one or two target creatures. They each get +2/+2 until end of turn.

Price of Freedom

Destroy target artifact or land an opponent controls. Its controller may search their library for a basic land card, put it onto the battlefield tapped, then shuffle.
Draw a card.

Resolute Blademaster

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

Plains

Wartime Protestors

Haste
Whenever another Ally you control enters, put a +1/+1 counter on that creature and it gains haste until end of turn.

Smellerbee, Rebel Fighter

First strike
Other creatures you control have haste.
Whenever Smellerbee attacks, you may discard your hand. If you do, draw cards equal to the number of attacking creatures.

Katara, Waterbending Master

Whenever you cast a spell during an opponent's turn, you get an experience counter.
Whenever Katara attacks, you may draw a card for each experience counter you have. If you do, discard a card.

Hada Freeblade

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

Steam Vents

({T}: Add {U} or {R}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Mystic Monastery

This land enters tapped.
{T}: Add {U}, {R}, or {W}.

Boomerang Basics

Return target nonland permanent to its owner's hand. If you controlled that permanent, draw a card.

Arcane Signet

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

Ondu Champion

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

Sulfur Falls

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

Earth Kingdom Protectors

Vigilance
Sacrifice this creature: Another target Ally you control gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)

Shivan Reef

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

Sol Ring

Yip Yip!

Target creature you control gets +2/+2 until end of turn. If that creature is an Ally, it also gains flying until end of turn.

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.

Airbender's Reversal

Choose one —
• Destroy target attacking creature.
• Airbend target creature you control. (Exile it. While it's exiled, its owner may cast it for {2} rather than its mana cost.)

Clifftop Retreat

This land enters tapped unless you control a Mountain or a Plains.
{T}: Add {R} or {W}.

Glacial Fortress

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

Adarkar Wastes

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

Redirect Lightning

As an additional cost to cast this spell, pay 5 life or pay {2}.
Change the target of target spell or ability with a single target.

Sea of Clouds

This land enters tapped unless you have two or more opponents.
{T}: Add {W} or {U}.

Hero of Goma Fada

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

Katara, Water Tribe's Hope

Vigilance
When Katara enters, create a 1/1 white Ally creature token.
Waterbend {X}: Creatures you control have base power and toughness X/X until end of turn. X can't be 0. Activate only during your turn. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)

Longshot, Rebel Bowman

Reach (This creature can block creatures with flying.)
Noncreature spells you cast cost {1} less to cast.
Whenever you cast a noncreature spell, Longshot deals 2 damage to each opponent.

Water Tribe Rallier

Waterbend {5}: Look at the top four cards of your library. You may reveal a creature card with power 3 or less from among them and put it into your hand. Put the rest on the bottom of your library in a random order. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)

Octopus Form

Target creature you control gets +1/+1 and gains hexproof until end of turn. Untap it. (It can't be the target of spells or abilities your opponents control.)

Mountain

Chakra Meditation

When this enchantment enters, return up to one target instant or sorcery card from your graveyard to your hand.
Whenever you cast an instant or sorcery spell, draw a card. Then discard a card unless there are three or more Lesson cards in your graveyard.

Chasm Guide

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

Sokka, Lateral Strategist

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

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.

Don't Have

Iroh, Dragon of the West

Haste
Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
At the beginning of combat on your turn, each creature you control with a counter on it gains firebending 2 until end of turn. (Whenever it attacks, add {R}{R}. This mana lasts until end of combat.)

Sokka, Bold Boomeranger

When Sokka enters, discard up to two cards, then draw that many cards.
Whenever you cast an artifact or Lesson spell, put a +1/+1 counter on Sokka.

Talisman of Conviction

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

Path to Exile

Exile target creature. Its controller may search their library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Avatar Enthusiasts

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

Sacred Foundry

({T}: Add {R} or {W}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Invasion Reinforcements

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

Accumulate Wisdom

Look at the top three cards of your library. Put one of those cards into your hand and the rest on the bottom of your library in any order. Put each of those cards into your hand instead if there are three or more Lesson cards in your graveyard.

Island

Talisman of Creativity

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

Whirlwind Technique

Target player draws two cards, then discards a card.
Airbend up to two target creatures. (To airbend a creature, exile it. While it's exiled, its owner may cast it for {2} rather than its mana cost.)

Kazuul Warlord

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

Raise the Palisade

Choose a creature type. Return all creatures that aren't of the chosen type to their owners' hands.

Aetherize

Return all attacking creatures to their owner's hand.

Kor Entanglers

Rally — Whenever this creature or another Ally you control enters, tap target creature an opponent controls.

Brainstorm

Draw three cards, then put two cards from your hand on top of your library in any order.

Raugrin Triome

({T}: Add {U}, {R}, or {W}.)
This land enters tapped.
Cycling {3} ({3}, Discard this card: Draw a card.)

Reckless Blaze

Reckless Blaze deals 5 damage to each creature. Whenever a creature you control dealt damage this way dies this turn, add {R}.

Seascape Aerialist

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

Exotic Orchard

Imprisoned in the Moon

Enchant creature, land, or planeswalker
Enchanted permanent is a colorless land with "{T}: Add {C}" and loses all other card types and abilities.

Consider

Surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
Draw a card.

Lightning Greaves

Equipped creature has haste and shroud. (It can't be the target of spells or abilities.)
Equip {0}

It'll Quench Ya!

Counter target spell unless its controller pays {2}.

Hallowed Fountain

({T}: Add {W} or {U}.)
As this land enters, you may pay 2 life. If you don't, it enters tapped.

Overwhelming Victory

Overwhelming Victory deals 5 damage to target creature. Each creature you control gains trample and gets +X/+0 until end of turn, where X is the amount of excess damage dealt this way.

Lantern Scout

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

That's Rough Buddy

Put a +1/+1 counter on target creature. Put two +1/+1 counters on that creature instead if a creature left the battlefield under your control this turn.
Draw a card.

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.

Abandon Attachments

You may discard a card. If you do, draw two cards.

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}.)

Command Tower

Sokka and Suki

Whenever Sokka and Suki or another Ally you control enters, attach up to one target Equipment you control to that creature.
Whenever an Equipment you control enters, create a 1/1 white Ally creature token.

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.