Stormsplitter + Sprout Swarm

Stormsplitter

Sprout Swarm

How it works

1. Cast Sprout Swarm with buyback by paying 4, reduced by 1 for each creature you can tap as you cast it.
2. Each Stormsplitter you control triggers, creating that many token copies of Stormsplitter.
3. Resolve Sprout Swarm, creating a 1/1 Saproling creature token and returning Sprout Swarm to your hand.
4. Repeat.