Retreat to Coralhelm + Walking Atlas + Boros Garrison

Retreat to Coralhelm

Walking Atlas

Boros Garrison

How it works

1. Activate Walking Atlas by tapping it, putting Boros Garrison from your hand onto the battlefield.
2. When Boros Garrison enters the battlefield, it and Retreat to Coralhelm trigger.
3. Resolve the Boros Garrison trigger, returning itself from the battlefield to your hand.
4. Resolve the Retreat to Coralhelm trigger, untapping Walking Atlas.
5. Repeat.