Retreat to Coralhelm + Arid Archway + PuPu UFO

Retreat to Coralhelm

Arid Archway

PuPu UFO

How it works

1. Activate PuPu UFO 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 PuPu UFO.
5. Repeat.