Didgeridoo + Cloudstone Curio + Mana Echoes

Didgeridoo

Cloudstone Curio

Mana Echoes

How it works

1. Activate Didgeridoo by paying 3, putting any nonartifact Minotaur from your hand onto the battlefield.
2. The Minotaur enters the battlefield, triggering Cloudstone Curio and Mana Echoes.
3. Resolve the Mana Echoes trigger, adding C for each Minotaur you control.
4. Resolve the Cloudstone Curio trigger, returning any other nontoken, nonartifact Minotaur from the battlefield to your hand.
5. Repeat.