Devoted Druid, Necklace of Girion, and Cloudstone Curio

Prerequisites

• Devoted Druid on the battlefield
• Necklace of Girion on the battlefield
• Cloudstone Curio on the battlefield

Steps

1. Activate Devoted Druid's first ability by tapping it, adding
2. Cast the creature castable for in your hand by paying its mana cost Necklace of Girion triggers, putting a +1/+1 counter on Devoted Druid
3. Resolve the creature spell
4. When the creature enters, Cloudstone Curio triggers, returning the other creature that's castable for from the battlefield to your hand
5. Activate Devoted Druid's second ability by putting a -1/-1 counter on it, untapping it
6. Repeat

Results

• Infinite ETB
• Infinite LTB
• Infinite storm count