Intruder Alarm, and Krenko, Mob Boss

Prerequisites

• Intruder Alarm on the battlefield
• Krenko, Mob Boss on the battlefield

Steps

1. Tap Krenko to activate it's ability, creating X goblin tokens where X is the number of Goblins you control
2. Token's ETB causes Intruder Alarm to trigger, untapping Krenko

Results

• Infinite ETB
• Infinite tokens