Incubation Druid + Cloudstone Curio + Rancor + Instill Energy

Incubation Druid

Cloudstone Curio

Rancor

Instill Energy

How it works

1. Activate Incubation Druid by tapping it, adding .
2. Activate Instill Energy by paying 0, untapping Incubation Druid.
3. Cast Rancor by paying , attaching it to Incubation Druid.
4. Rancor enters the battlefield, triggering Cloudstone Curio, returning Instill Energy from the battlefield to your hand.
5. Cast Instill Energy by paying , attaching it to Incubation Druid.
6. Instill Energy enters the battlefield, triggering Cloudstone Curio, returning Rancor from the battlefield to your hand.
7. Repeat.