Have

Fire Nation Cadets

This creature has firebending 2 as long as there's a Lesson card in your graveyard. (Whenever this creature attacks, add {R}{R}. This mana lasts until end of combat.)
{2}: This creature gets +1/+0 until end of turn.

Uncle Iroh

Firebending 1 (Whenever this creature attacks, add {R}. This mana lasts until end of combat.)
Lesson spells you cast cost {1} less to cast.

Hermitic Herbalist

{T}: Add one mana of any color.
{T}: Add two mana in any combination of colors. Spend this mana only to cast Lesson spells.

Dragonfly Swarm

Flying, ward {1} (Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays {1}.)
This creature's power is equal to the number of noncreature, nonland cards in your graveyard.
When this creature dies, if there's a Lesson card in your graveyard, draw a card.

First-Time Flyer

Flying
This creature gets +1/+1 as long as there's a Lesson card in your graveyard.

It'll Quench Ya!

Counter target spell unless its controller pays {2}.

Mountain

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.

Toph, Hardheaded Teacher

When Toph enters, you may discard a card. If you do, return target instant or sorcery card from your graveyard to your hand.
Whenever you cast a spell, earthbend 1. If that spell is a Lesson, put an additional +1/+1 counter on that land. (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.)

Omashu City

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

Forest

Platypus-Bear

Defender
When this creature enters, mill two cards. (Put the top two cards of your library into your graveyard.)
As long as there is a Lesson card in your graveyard, this creature can attack as though it didn't have defender.

Abandon Attachments

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

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.)

Iroh, Grand Lotus

Firebending 2
During your turn, each non-Lesson instant and sorcery card in your graveyard has flashback. The flashback cost is equal to that card's mana cost. (You may cast a card from your graveyard for its flashback cost. Then exile it.)
During your turn, each Lesson card in your graveyard has flashback {1}.

Airship Engine Room

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

Island

Cycle of Renewal

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

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.)