How can you create a combo with Prototype Portal, Retreat to Coralhelm, Ensoul Artifact, Darksteel Citadel?
user
[START OF COMBO]This combo can be formed with Prototype Portal, Retreat to Coralhelm, Ensoul Artifact, Darksteel Citadel

Color identity: U
Mana cost: 
Steps:
  1. Activate Prototype Portal by tapping it, creating a token copy of Darksteel Citadel.
  2. When the Darksteel Citadel token enters the battlefield, Retreat to Coralhelm triggers, untapping Prototype Portal.
  3. Repeat.[END OF COMBO STEPS]

Result:
  - Infinite colorless mana
  - Infinite Darksteel Citadel tokens
  - Infinite landfall triggers[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - Prototype Portal must be on the battlefield
  - Retreat to Coralhelm must be on the battlefield
  - Ensoul Artifact must be on the battlefield
  - Darksteel Citadel must be exiled
  - Ensoul Artifact attached to Prototype Portal.
  - Prototype Portal does not have summoning sickness.
[END OF COMBO PREREQUISITES]
assistant