Consider

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

Swamp

Fire Nation's Conquest

Dark Depths

Dark Depths enters with ten ice counters on it.
{3}: Remove an ice counter from Dark Depths.
When Dark Depths has no ice counters on it, sacrifice it. If you do, create Marit Lage, a legendary 20/20 black Avatar creature token with flying and indestructible.

Sokka's Charge

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

Hog-Monkey

At the beginning of combat on your turn, target creature you control with a +1/+1 counter on it gains menace until end of turn. (It can't be blocked except by two or more creatures.)
Exhaust — {5}: Put two +1/+1 counters on this creature. (Activate each exhaust ability only once.)

Mongoose Lizard

Menace (This creature can't be blocked except by two or more creatures.)
When this creature enters, it deals 1 damage to any target.
Mountaincycling {2} ({2}, Discard this card: Search your library for a Mountain card, reveal it, put it into your hand, then shuffle.)

Fated Firepower

Flash
This enchantment enters with X fire counters on it.
If a source you control would deal damage to an opponent or a permanent an opponent controls, it deals that much damage plus an amount of damage equal to the number of fire counters on this enchantment instead.

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.

Bender's Waterskin

Untap this artifact during each other player's untap step.
{T}: Add one mana of any color.

Kyoshi Island Plaza

When Kyoshi Island Plaza enters, search your library for up to X basic land cards, where X is the number of Shrines you control. Put those cards onto the battlefield tapped, then shuffle.
Whenever another Shrine you control enters, search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Volcanic Torrent

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
Volcanic Torrent deals X damage to each creature and planeswalker your opponents control, where X is the number of spells you've cast this turn.

Wan Shi Tong, All-Knowing

Flying
When Wan Shi Tong enters, target nonland permanent's owner puts it into their library second from the top or on the bottom.
Whenever one or more cards are put into a library from anywhere, create two 1/1 colorless Spirit creature tokens with "This token can't block or be blocked by non-Spirit creatures."

Benevolent River Spirit

As an additional cost to cast this spell, waterbend {5}. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)
Flying, ward {2} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {2}.)
When this creature enters, scry 2.

Treetop Village

This land enters tapped.
{T}: Add {G}.
{1}{G}: This land becomes a 3/3 green Ape creature with trample until end of turn. It's still a land. (It can deal excess combat damage to the player or planeswalker it's attacking.)

Scarring Memories

You may cast this spell as though it had flash if you control an attacking legendary creature.
Target opponent sacrifices a creature of their choice, discards a card, and loses 3 life.

Anguished Unmaking

Exile target nonland permanent. You lose 3 life.

Frog-Squirrels

Reach (This creature can block creatures with flying.)

Hama, the Bloodbender

When Hama enters, target opponent mills three cards. Exile up to one noncreature, nonland card from that player's graveyard. For as long as you control Hama, you may cast the exiled card during your turn by waterbending {X} rather than paying its mana cost, where X is its mana value. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)

Rebellious Captives

Exhaust — {6}: Put two +1/+1 counters on this creature, then 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. Activate each exhaust ability only once.)

Sokka, Wolf Cove's Protector

Vigilance (Attacking doesn't cause this creature to tap.)

Thriving Heath

This land enters tapped. As it enters, choose a color other than white.
{T}: Add {W} or one mana of the chosen color.

Release to Memory

Exile target opponent's graveyard. For each creature card exiled this way, create a 1/1 colorless Spirit creature token.

Brought Back

Choose up to two target permanent cards in your graveyard that were put there from the battlefield this turn. Return them to the battlefield tapped.

Shared Roots

Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Suspicious Bookcase

Defender
{3}, {T}: Target creature can't be blocked this turn.

Bribery

Search target opponent's library for a creature card and put that card onto the battlefield under your control. Then that player shuffles.

Turtle-Duck

{3}: Until end of turn, this creature has base power 4 and gains trample.

Island

Desperate Plea

As an additional cost to cast this spell, sacrifice a creature.
Choose one or both —
• Return target creature card from your graveyard to the battlefield if its power is less than or equal to the sacrificed creature's power.
• Destroy target creature.

Rites of Flourishing

At the beginning of each player's draw step, that player draws an additional card.
Each player may play an additional land on each of their turns.

Toph, the First Metalbender

Nontoken artifacts you control are lands in addition to their other types. (They don't gain the ability to {T} for mana.)
At the beginning of your end step, 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.)

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.)

Ozai's Cruelty

Ozai's Cruelty deals 2 damage to target player. That player discards two cards.

Uncle's Musings

Converge — Return up to X permanent cards from your graveyard to your hand, where X is the number of colors of mana spent to cast this spell.
Exile Uncle's Musings.

Katara, Heroic Healer

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
When Katara enters, put a +1/+1 counter on each other creature you control.

Tolls of War

When this enchantment enters, create a Clue token. (It's an artifact with "{2}, Sacrifice this token: Draw a card.")
Whenever you sacrifice a permanent during your turn, create a 1/1 white Ally creature token. This ability triggers only once each turn.

Meltdown

Destroy each artifact with mana value X or less.

Pretending Poxbearers

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

Boiling Rock Prison

This land enters tapped.
{T}: Add {B} or {R}.
{4}, {T}, Sacrifice this land: Draw a card.

Day of Black Sun

Each creature with mana value X or less loses all abilities until end of turn. Destroy those creatures.

Boomerang Basics

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

Merchant of Many Hats

{2}{B}: Return this card from your graveyard to your hand.

Cycle of Renewal

Sacrifice a land. Search your library for up to two basic land cards, put them onto the battlefield tapped, then shuffle.

Preordain

Scry 2, then draw a card. (To scry 2, look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

Monk Gyatso

Whenever another creature you control becomes the target of a spell or ability, you may airbend that creature. (Exile it. While it's exiled, its owner may cast it for {2} rather than its mana cost.)

Many Partings

Search your library for a basic land card, reveal it, put it into your hand, then shuffle. Create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this token: You gain 3 life.")

The Last Agni Kai

Target creature you control fights target creature an opponent controls. If the creature the opponent controls is dealt excess damage this way, add that much {R}.
Until end of turn, you don't lose unspent red mana as steps and phases end.

Raven Eagle

Flying
Whenever this creature enters or attacks, exile up to one target card from a graveyard. If a creature card is exiled this way, create a Clue token. (It's an artifact with "{2}, Sacrifice this token: Draw a card.")
Whenever you draw your second card each turn, each opponent loses 1 life and you gain 1 life.

Mystic Remora

Cumulative upkeep {1} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays {4}.

Foggy Swamp Visions

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 creature cards from graveyards. For each creature card exiled this way, create a token that's a copy of it. At the beginning of your next end step, sacrifice those tokens.

Cracked Earth Technique

Earthbend 3, then earthbend 3. You gain 3 life. (To earthbend 3, target land you control becomes a 0/0 creature with haste that's still a land. Put three +1/+1 counters on it. When it dies or is exiled, return it to the battlefield tapped.)

Sparring Dummy

Defender
{T}: Mill a card. You may put a land card milled this way into your hand. You gain 2 life if a Lesson card is milled this way. (Το mill a card, put the top card of your library into your graveyard.)

Badgermole Cub

When this creature 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.)
Whenever you tap a creature for mana, add an additional {G}.

Seismic Sense

Look at the top X cards of your library, where X is the number of lands you control. You may reveal a creature or land card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.

Black Sun's Zenith

Put X -1/-1 counters on each creature. Shuffle Black Sun's Zenith into its owner's library.

Agna Qel'a

This land enters tapped unless you control a basic land.
{T}: Add {U}.
{2}{U}, {T}: Draw a card, then discard a card.

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.

Ozai, the Phoenix King

Trample, firebending 4, haste
If you would lose unspent mana, that mana becomes red instead.
Ozai has flying and indestructible as long as you have six or more unspent mana.

Iroh, Firebending Instructor

Whenever Iroh attacks, attacking creatures get +1/+1 until end of turn.

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.

Silence

Your opponents can't cast spells this turn.

Leaves from the Vine

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Mill three cards, then create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this token: You gain 3 life.")
II — Put a +1/+1 counter on each of up to two target creatures you control.
III — Draw a card if there's a creature or Lesson card in your graveyard.

Humble Defector

{T}: Draw two cards. Target opponent gains control of this creature. Activate only during your turn.

Airship Engine Room

This land enters tapped.
{T}: Add {U} or {R}.
{4}, {T}, Sacrifice this land: Draw a card.

Scout's Warning

The next creature card you play this turn can be played as though it had flash.
Draw a card.

Hei Bai, Spirit of Balance

Whenever Hei Bai enters or attacks, you may sacrifice another creature or artifact. If you do, put two +1/+1 counters on Hei Bai.
When Hei Bai leaves the battlefield, put its counters on target creature you control.

Sold Out

Exile target creature. If it was dealt damage this turn, create a Clue token. (It's an artifact with "{2}, Sacrifice this token: Draw a card.")

Rocky Rebuke

Target creature you control deals damage equal to its power to target creature an opponent controls.

Join the Dance

Create two 1/1 white Human creature tokens.
Flashback {3}{G}{W} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Cruel Tutor

Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Painful Truths

Converge — You draw X cards and you lose X life, where X is the number of colors of mana spent to cast this spell.

Roku's Mastery

Roku's Mastery deals X damage to target creature. If X is 4 or greater, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)

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.

Entomb

Search your library for a card, put that card into your graveyard, then shuffle.

Aang, Master of Elements

Flying
Spells you cast cost {W}{U}{B}{R}{G} less to cast.
At the beginning of each upkeep, you may transform Aang, Master of Elements. If you do, you gain 4 life, draw four cards, put four +1/+1 counters on him, and he deals 4 damage to each opponent.

Avatar Aang

Flying, firebending 2
Whenever you waterbend, earthbend, firebend, or airbend, draw a card. Then if you've done all four this turn, transform Avatar Aang.

Avatar Aang // Aang, Master of Elements

Heartless Act

Choose one —
• Destroy target creature with no counters on it.
• Remove up to three counters from target creature.

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.

White Lotus Reinforcements

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

Flexible Waterbender

Vigilance
Waterbend {3}: This creature has base power and toughness 5/2 until end of turn. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)

Nature's Claim

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

Crescent Island Temple

When Crescent Island Temple enters, for each Shrine you control, create a 1/1 red Monk creature token with prowess. (Whenever you cast a noncreature spell, it gets +1/+1 until end of turn.)
Whenever another Shrine you control enters, create a 1/1 red Monk creature token with prowess.

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.

Northern Air Temple

When Northern Air Temple enters, each opponent loses X life and you gain X life, where X is the number of Shrines you control.
Whenever another Shrine you control enters, each opponent loses 1 life and you gain 1 life.

Saber-Tooth Moose-Lion

Reach
Forestcycling {2} ({2}, Discard this card: Search your library for a Forest card, reveal it, put it into your hand, then shuffle.)

Wolfbat

Flying
Whenever you draw your second card each turn, you may pay {B}. If you do, return this card from your graveyard to the battlefield with a finality counter on it. (If a creature with a finality counter on it would die, exile it instead.)

Geyser Leaper

Flying
Waterbend {4}: Draw a card, then discard a card. (While paying a waterbend cost, you can tap your artifacts and creatures to help. Each one pays for {1}.)

Sandbenders' Storm

Choose one—
• Destroy target creature with power 4 or greater.
• Earthbend 3. (Target land you control becomes a 0/0 creature with haste that's still a land. Put three +1/+1 counters on it. When it dies or is exiled, return it to the battlefield tapped.)

Firebender Ascension

When this enchantment enters, create a 2/2 red Soldier creature token with firebending 1.
Whenever a creature you control attacking causes a triggered ability of that creature to trigger, put a quest counter on this enchantment. Then if it has four or more quest counters on it, you may copy that ability. You may choose new targets for the copy.

Blood Moon

Thespian's Stage

{T}: Add {C}.
{2}, {T}: This land becomes a copy of target land, except it has this ability.

Great Divide Guide

Each land and Ally you control has "{T}: Add one mana of any color."

Zhao, the Moon Slayer

Menace
Nonbasic lands enter tapped.
{7}: Put a conqueror counter on Zhao.
As long as Zhao has a conqueror counter on him, nonbasic lands are Mountains. (They lose all other land types and abilities and have "{T}: Add {R}.")

The Walls of Ba Sing Se

Defender
Other permanents you control have indestructible.

Chain of Vapor

Return target nonland permanent to its owner's hand. Then that permanent's controller may sacrifice a land of their choice. If the player does, they may copy this spell and may choose a new target for that copy.

The Spirit Oasis

When The Spirit Oasis enters, draw a card for each Shrine you control.
Whenever another Shrine you control enters, draw a card.

Earthbending Lesson

Earthbend 4. (Target land you control becomes a 0/0 creature with haste that's still a land. Put four +1/+1 counters on it. When it dies or is exiled, return it to the battlefield tapped.)

Zuko, Seeking Honor

Firebending 1 (Whenever this creature attacks, add {R}. This mana lasts until end of combat.)
Whenever you cast a noncreature spell, Zuko gains first strike until end of turn.
Whenever Zuko deals combat damage to a player, put a +1/+1 counter on him.

Prosperity

Compassionate Healer

Whenever this creature becomes tapped, you gain 1 life and scry 1. (Look at the top card of your library. You may put it on the bottom.)

Putrefy

Destroy target artifact or creature. It can't be regenerated.

Fire Nation Raider

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