Requires

Spellbinding Soprano must be in the graveyard. Sprout Swarm must be in hand. Runaway Steam-Kin must be on the battlefield. Mana needed: , plus an additional available, where X is equal to three minus the number of +1/+1 counters on Runaway Steam-Kin

Steps

1. Activate Spellbinding Soprano's encore ability by paying 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 less to cast for each Spellbinding Soprano token.
4. If Runaway Steam-Kin has three or more +1/+1 counters on it, activate its ability by removing three +1/+1 counters from it, adding .
5. Cast Sprout Swarm by paying and tapping a green creature you control.
6. Runaway Steam-Kin triggers, putting a +1/+1 counter on itself.
7. Resolve Sprout Swarm, creating a 1/1 Saproling creature token and returning Sprout Swarm to your hand.
8. Repeat from step 4.

Results