Prototype Portal, Retreat to Coralhelm, Ensoul Artifact, and Darksteel Citadel

Prerequisites

• Prototype Portal on the battlefield
• Retreat to Coralhelm on the battlefield
• Ensoul Artifact on the battlefield
• Darksteel Citadel in exile

Steps

1. Activate Prototype Portal by tapping it, creating a token copy of Darksteel Citadel
2. When the Darksteel Citadel token enters the battlefield, Retreat to Coralhelm triggers, untapping Prototype Portal
3. Repeat

Results

• Infinite colorless mana
• Infinite Darksteel Citadel tokens
• Infinite landfall triggers