Spellbinding Soprano + Sprout Swarm + Deekah, Fractal Theorist

Spellbinding Soprano

Sprout Swarm

Deekah, Fractal Theorist

How it works

1. Activate Spellbinding Soprano's encore ability by paying 3 and exiling it from your graveyard, creating a token copy of it with haste for each opponent you have.
2. Declare each Spellbinding Soprano token as an attacker.
3. Each Spellbinding Soprano token triggers, causing instant and sorcery spells you cast this turn to cost 1 less to cast for each Spellbinding Soprano token.
4. Cast Sprout Swarm with buyback by paying 1 and tapping a green creature you control.
5. Deekah triggers, creating a 0/0 Fractal creature token, then putting two +1/+1 counters on it, Resolve Sprout Swarm, creating a 1/1 Saproling creature token and returning Sprout Swarm to your hand.
6. Cast Sprout Swarm with buyback by tapping the Saporling and Fractal tokens.
7. Repeat from step 5.

This intricate loop turns a graveyard into an explosive engine by utilizing Spellbinding Soprano's encore ability to massively discount your instant and sorcery spells through its attacking trigger. With those cost reductions online, Sprout Swarm becomes free to cast repeatedly because its buyback cost is offset and its convoke ability lets your newly minted creatures pitch in. Meanwhile, Deekah, Fractal Theorist acts as the ultimate amplifier, triggering off every single casting of Sprout Swarm to continuously grow an unstoppable army of unblockable tokens.