How can you create a combo with Prototype Portal, Clock of Omens, Grinding Station, Darksteel Citadel?
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[START OF COMBO]This combo can be formed with Prototype Portal, Clock of Omens, Grinding Station, Darksteel Citadel

Color identity: C
Mana cost: 
Steps:
  1. Activate Prototype Portal by paying {0} 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.[END OF COMBO STEPS]

Result:
  - Infinite landfall triggers
  - Infinite tapped land tokens[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - Prototype Portal must be on the battlefield
  - Clock of Omens must be on the battlefield
  - Grinding Station must be on the battlefield
  - Darksteel Citadel must be exiled
[END OF COMBO PREREQUISITES]
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