Xavier Sal, Infested Captain, Intruder Alarm, and Railway Brawler

Prerequisites

• Xavier Sal, Infested Captain on the battlefield
• Intruder Alarm on the battlefield
• Railway Brawler on the battlefield
• There is at least one counter on a permanent you control
• You control at least one creature token with power 1 or greater

Steps

1. Activate Xavier Sal's first ability by tapping it and removing a counter from a permanent you control, creating a copy of any creature token you control with power 1 or greater
2. When the creature token enters the battlefield, Intruder Alarm and Railway Brawler trigger
3. Resolve the Intruder Alarm trigger, untapping all creatures
4. Resolve the Railway Brawler trigger, putting at least one +1/+1 counter on the creature token
5. Repeat

Results

• Infinite creature tokens
• Infinite ETB
• Infinite mana creatures you control can produce
• Infinite untap of all creatures