Prototype Portal + Clock of Omens + Grinding Station + Ancient Den

Prototype Portal
Clock of Omens
Grinding Station
Ancient Den

Requires
Ancient Den exiled by Prototype Portal. All other permanents on the battlefield.
Steps
  1. Activate Prototype Portal by paying 0 and tapping it, creating a token copy of Ancient Den
  2. The Ancient Den token enters, triggering Grinding Station, untapping Grinding Station
  3. Activate Clock of Omens by tapping the Ancient Den token and Grinding Station, untapping Prototype Portal
  4. Repeat
Results
Infinite landfall triggers. Infinite tapped land tokens.