Cloudstone Curio + Beastcaller Savant + Bosk Banneret + Kobolds of Kher Keep

Cloudstone Curio

Beastcaller Savant

Bosk Banneret

Kobolds of Kher Keep

How it works

1. Activate Beastcaller Savant by tapping it, adding that can only be spent to cast a creature spell.
2. Cast Kobolds of Kher Keep by paying 0.
3. When Kobolds of Kher Keep enters the battlefield, Cloudstone Curio triggers, returning Beastcaller Savant to your hand from the battlefield.
4. Cast Beastcaller Savant by paying due to Bosk Banneret.
5. When Beastcaller Savant enters the battlefield, Cloudstone Curio triggers, returning Kobolds of Kher Keep to your hand from the battlefield.
6. Repeat.