Retreat to Coralhelm + Scaled Herbalist + Arid Archway

Retreat to Coralhelm

Scaled Herbalist

Arid Archway

How it works

1. Activate Scaled Herbalist by tapping it, putting Arid Archway from your hand onto the battlefield.
2. When Arid Archway enters the battlefield, it and Retreat to Coralhelm trigger.
3. Resolve the Arid Archway trigger, returning itself from the battlefield to your hand.
4. Resolve the Retreat to Coralhelm trigger, untapping Scaled Herbalist.
5. Repeat.