Sprout Swarm + Ashnod's Altar + Anointed Procession

Sprout Swarm

Ashnod's Altar

Anointed Procession

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 loop is a masterclass in self-sustaining token generation, perfectly fueled by the colorless mana engine of Ashnod's Altar. By using the altar to sacrifice the Saprolings produced by Sprout Swarm, you generate all the mana needed to keep casting the spell with its buyback cost. The true engine multiplier here is Anointed Procession, which doubles your token output so that every single iteration leaves you with a surplus of creatures to sacrifice for profit and tap for convoke.