Prototype Portal, Clock of Omens, Grinding Station, and Darksteel Citadel

Prerequisites

• Prototype Portal on the battlefield
• Clock of Omens on the battlefield
• Grinding Station on the battlefield
• Darksteel Citadel in exile

Steps

1. Activate Prototype Portal by paying and tapping it, creating a token copy of Darksteel Citadel
2. The Darksteel Citadel token enters, triggering Grinding Station, untapping Grinding Station
3. Activate Clock of Omens by tapping the Darksteel Citadel token and Grinding Station, untapping Prototype Portal
4. Repeat

Results

• Infinite landfall triggers
• Infinite tapped land tokens