Scaretiller, Retreat to Coralhelm, Gateway Plaza, and Urza, Lord High Artificer

Prerequisites

• Scaretiller on the battlefield
• Retreat to Coralhelm on the battlefield
• Gateway Plaza in the graveyard
• Urza, Lord High Artificer on the battlefield

Steps

1. Activate Urza by tapping Scaretiller, adding
2. Scaretiller triggers, returning Gateway Plaza from your graveyard to the battlefield tapped
3. Gateway Plaza enters the battlefield, triggering itself and Retreat to Coralhelm
4. Resolve the Gateway Plaza trigger, choosing to sacrifice it
5. Resolve the Retreat to Coralhelm trigger, untapping Scaretiller
6. Repeat

Results

• Infinite blue mana
• Infinite landfall triggers
• Infinite tap triggers
• Play all cards in your library without paying their mana costs
• Exile your library
• Cast all cards in your library without paying their mana costs