Prototype Portal + Clock of Omens + Battered Golem + Ancient Den

Prototype Portal
Clock of Omens
Battered Golem
Ancient Den

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