Murasa Rootgrazer, Retreat to Coralhelm, and Mirrormade

Prerequisites

• Murasa Rootgrazer on the battlefield
• Retreat to Coralhelm on the battlefield
• Mirrormade on the battlefield
• At least one basic land in hand
• Mirrormade is a copy of Retreat to Coralhelm
• Murasa Rootgrazer does not have summoning sickness

Steps

1. Activate Murasa Rootgrazer's first ability, putting a basic land from your hand onto the battlefield
2. The Retreat to Coralhelms trigger
3. In response, activate the basic land by tapping it, adding
4. Let the first Retreat to Coralhelm trigger resolve, untapping Murasa Rootgrazer
5. Activate Murasa Rootgrazer's last ability, returning any basic land you control from the battlefield to your hand
6. Let the second Retreat trigger resolve, untapping Murasa Rootgrazer
7. Repeat

Results

• Infinite landfall triggers
• Infinite mana basic lands you control can produce