Urza, Prince of Kroog, Metalworker, Retreat to Coralhelm, and Darksteel Citadel

Prerequisites

• Urza, Prince of Kroog on the battlefield
• Metalworker on the battlefield
• Retreat to Coralhelm on the battlefield
• Darksteel Citadel on the battlefield
• You have at least three artifact cards in hand
• Metalworker does not have summoning sickness

Steps

1. Activate Metalworker by tapping it and revealing at least three artifact cards from your hand, adding at least six
2. Activate Urza by paying , creating a token copy of Darksteel Citadel that is a 1/1 Soldier
3. When the Darksteel Citadel token enters the battlefield, Retreat to Coralhelm triggers, untapping Metalworker
4. Repeat
5. If you have four or more artifact cards in hand, this combo nets infinite colorless mana, and you may target any artifact you control to get infinite copies of them

Results

• Infinite colorless mana
• Infinite copies of each artifact you control
• Infinite creature tokens
• Infinite ETB
• Infinite landfall triggers