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 .
Iroh turns your graveyard into a second hand: during your turn every instant/sorcery there gains flashback for its mana cost, and every Lesson gets flashback . You fill the yard with cantrips, removal, and big spells, then chain double-spells per turn for relentless card advantage and a spell-based or storm-style finish. Early turns are setup (ramp, card draw, self-mill); mid-game you start recasting your best spells every turn while attacking for Firebending value.
Built-in recursion engine means you almost never run out of gas—every spell is essentially castable twice.
Free flashback on Lessons makes a Learn/Lesson subtheme extremely efficient.
Temur gives access to ramp, card advantage, and the best burn/removal/X-spells to abuse the recursion.
Synergizes with self-mill and discard, turning 'wasted' cards in the yard into resources.
You pay full mana cost for non-Lesson flashback, so it's value rather than a free combo—mana-hungry.
Heavily commander-dependent; if Iroh is removed repeatedly the engine stalls.