Goblin Welder, Retreat to Coralhelm, Darksteel Citadel, and Great Furnace

Prerequisites

• Goblin Welder on the battlefield
• Retreat to Coralhelm on the battlefield
• Darksteel Citadel in the graveyard
• Great Furnace on the battlefield
• Goblin Welder does not have summoning sickness

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
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
7. Repeat

Results

• Infinite colorless mana
• Infinite landfall triggers
• Infinite red mana