Prototype Portal, Retreat to Coralhelm, Ensoul Artifact, and Great Furnace

Prerequisites

• Prototype Portal on the battlefield
• Retreat to Coralhelm on the battlefield
• Ensoul Artifact on the battlefield
• Great Furnace in exile

Steps

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

Results

• Infinite Great Furnace tokens
• Infinite landfall triggers
• Infinite red mana