How can you create a combo with Goblin Welder, Retreat to Coralhelm, Darksteel Citadel, Great Furnace?
user
[START OF COMBO]This combo can be formed with Goblin Welder, Retreat to Coralhelm, Darksteel Citadel, Great Furnace

Color identity: UR
Mana cost: 
Steps:
  1. Activate Goblin Welder by tapping it, causing you to sacrifice Great Furnace and return Darksteel Citadel from your graveyard to the battlefield.
  2. Darksteel Citadel enters the battlefield, triggering Retreat to Coralhelm, untapping Goblin Welder.
  3. Activate Darksteel Citadel by tapping it, adding {C}.
  4. Activate Goblin Welder by tapping it, causing you to sacrifice Darksteel Citadel and return Great Furnace from your graveyard to the battlefield.
  5. Great Furnace enters the battlefield, triggering Retreat to Coralhelm, untapping Goblin Welder.
  6. Activate Great Furnace by tapping it, adding {R}.
  7. Repeat.[END OF COMBO STEPS]

Result:
  - Infinite colorless mana
  - Infinite landfall triggers
  - Infinite red mana[END OF COMBO RESULT][END OF COMBO]

Other prerequisites:
  - Goblin Welder must be on the battlefield
  - Retreat to Coralhelm must be on the battlefield
  - Darksteel Citadel must be in the graveyard
  - Great Furnace must be on the battlefield
  - Goblin Welder does not have summoning sickness.
[END OF COMBO PREREQUISITES]
assistant