Retreat to Coralhelm + Llanowar Scout + Simic Growth Chamber

Retreat to Coralhelm

Llanowar Scout

Simic Growth Chamber

How it works

1. Activate Llanowar Scout by tapping it, putting Simic Growth Chamber from your hand onto the battlefield.
2. When Simic Growth Chamber enters the battlefield, it and Retreat to Coralhelm trigger.
3. Resolve the Simic Growth Chamber trigger, returning itself from the battlefield to your hand.
4. Resolve the Retreat to Coralhelm trigger, untapping Llanowar Scout.
5. Repeat.