Necroduality + Rooftop Storm + Cloudstone Curio

Necroduality

Rooftop Storm

Cloudstone Curio

How it works

1. Cast a nonlegendary, nonartifact Zombie by paying 0.
2. The Zombie enters the battlefield, triggering Cloudstone Curio and Necroduality.
3. Resolve the Cloudstone Curio trigger, returning nothing to your hand.
4. Resolve the Necroduality trigger, creating a token copy of the Zombie.
5. Cloudstone Curio triggers, returning the nontoken Zombie to your hand.
6. Repeat.