Retreat to Coralhelm + Llanowar Scout + Boros Garrison

Retreat to Coralhelm

Llanowar Scout

Boros Garrison

How it works

1. Activate Llanowar Scout 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 Llanowar Scout.
5. Repeat.