Retreat to Coralhelm + Trench Behemoth + Llanowar Scout

Retreat to Coralhelm

Trench Behemoth

Llanowar Scout

How it works

1. Activate Trench Behemoth by returning a land from the battlefield to your hand, untapping Trench Behemoth.
2. Activate Llanowar Scout by tapping it, putting the land from your hand onto the battlefield.
3. When the land enters the battlefield, Retreat to Coralhelm triggers, untapping Llanowar Scout.
4. If the land enters untapped and can produce mana, you may activate it by tapping it, adding at least 1.
5. Repeat.