Spellbinding Soprano | Sprout Swarm | Runaway Steam-Kin

Cards

({3} magic symbol) ({R} magic symbol) , plus an additional ({X} magic symbol) available, where X is equal to three minus the number of +1/+1 counters on
Runaway Steam-Kin available.

Activate
Spellbinding Soprano's encore ability by paying ({3} magic symbol) ({R} magic symbol) and exiling it from your graveyard, creating a token copy of it with haste for each opponent you have.
Declare each
Spellbinding Soprano token as an attacker.
Each
Spellbinding Soprano token triggers, causing instant and sorcery spells you cast this turn to cost ({1} magic symbol) less to cast for each
Spellbinding Soprano token.
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 ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) .
Cast
Sprout Swarm by paying ({1} magic symbol) and tapping a green creature you control.
Runaway Steam-Kin triggers, putting a +1/+1 counter on itself.
Resolve
Sprout Swarm, creating a 1/1 Saproling creature token and returning
Sprout Swarm to your hand.
Repeat from step 4.