Arni Metalbrow, Thousand-Faced Shadow, Cloudstone Curio, and Priest of Urabrask

Prerequisites

• Arni Metalbrow on the battlefield
• Thousand-Faced Shadow in hand
• Cloudstone Curio on the battlefield
• Priest of Urabrask on the battlefield
• Priest of Urabrask does not have summoning sickness
• available

Steps

1. Declare Priest of Urabrask as an attacker
2. Arni Metalbrow triggers, causing you to pay to put Thousand-Faced Shadow from your hand onto the battlefield tapped and attacking
3. When Thousand-Faced Shadow enters the battlefield, it, Arni Metalbrow and Cloudstone Curio trigger
4. Resolve the Cloudstone Curio trigger, choosing to return nothing to your hand from the battlefield
5. Resolve the Arni Metalbrow trigger, choosing not to pay
6. Resolve the Thousand-Faced Shadow trigger, creating a token copy of Priest of Urabrask that enters the battlefield tapped and attacking
7. When the Priest of Urabrask token enters the battlefield, it, Arni Metalbrow and Cloudstone Curio trigger
8. Resolve the Priest of Urabrask trigger, adding
9. Resolve the Cloudstone Curio trigger, returning Thousand-Faced Shadow to your hand from the battlefield
10. Resolve the Arni Metalbrow trigger, causing you to pay to put Thousand-Faced Shadow from your hand onto the battlefield tapped and attacking
11. Repeat from step 3

Results

• Infinite ETB
• Infinite LTB
• Infinite red mana
• Infinite tapped creature tokens that are attacking