Ancient Den, Goblin Welder, Retreat to Coralhelm, and Seat of the Synod

Prerequisites

• Ancient Den on the battlefield
• Goblin Welder on the battlefield
• Retreat to Coralhelm on the battlefield
• Seat of the Synod in your graveyard
• Goblin Welder does not have summoning sickness

Steps

1. Activate Goblin Welder by tapping it, causing you to sacrifice Ancient Den 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 Ancient Den from your graveyard to the battlefield
5. Ancient Den enters the battlefield, triggering Retreat to Coralhelm, untapping Goblin Welder
6. Activate Ancient Den by tapping it, adding
7. Repeat

Results

• Infinite blue mana
• Infinite landfall triggers
• Infinite white mana