Spellbinding Soprano, Sprout Swarm, and Birgi, God of Storytelling // Harnfel, Horn of Bounty

Prerequisites

• Spellbinding Soprano in the graveyard
• Sprout Swarm in hand
• Birgi, God of Storytelling // Harnfel, Horn of Bounty on the battlefield
• You have at least three opponents
• You control an untapped green creature
• available

Steps

1. Activate Spellbinding Soprano's encore ability by paying and exiling it from your graveyard, creating two token copies 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. Cast Sprout Swarm with buyback by paying and tapping a green creature you control
5. Birgi triggers, adding
6. Resolve Sprout Swarm, creating a 1/1 Saproling creature token and returning Sprout Swarm to your hand
7. Repeat from step 4

Results

• Infinite ETB
• Infinite magecraft triggers
• Infinite storm count
• Infinite tapped creature tokens