Sprout Swarm + Ashnod's Altar + Bard, King of Dale

Sprout Swarm

Ashnod's Altar

Bard, King of Dale

How it works

1. Cast Sprout Swarm with buyback by paying at most 4, creating two creature tokens and returning Sprout Swarm from the battlefield to your hand.
2. Cast Sprout Swarm with buyback by paying at most 3 and tapping two creature tokens, creating two creature tokens and returning Sprout Swarm from the battlefield to your hand.
3. Activate Ashnod's Altar twice by sacrificing two tapped creature tokens, adding CCCC
4. Repeat from step 2.

This charming loop relies on Bard, King of Dale's powerful replacement effect, which doubles any token generation to ensure that casting Sprout Swarm yields twice as many Saprolings as intended. Those freshly minted creatures can immediately be tapped to help pay for Sprout Swarm's convoke cost, while the buyback ability ensures the spell continuously returns to your hand rather than the graveyard. Finally, Ashnod's Altar provides the engine to sacrifice those creatures for a tidy profit of colorless mana, fueling subsequent casts and generating infinite resources.