Goblin Welder, Retreat to Coralhelm, Seat of the Synod, and Great Furnace

Prerequisites

• Goblin Welder on the battlefield
• Retreat to Coralhelm on the battlefield
• Seat of the Synod 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 Seat of the Synod from your graveyard to the battlefield
2. Seat of the Synod enters the battlefield, triggering Retreat to Coralhelm, untapping Goblin Welder
3. Activate Seat of the Synod by tapping it, adding
4. Activate Goblin Welder by tapping it, causing you to sacrifice Seat of the Synod 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 blue mana
• Infinite landfall triggers
• Infinite red mana