Intruder Alarm, and Thraben Doomsayer

Prerequisites

• Intruder Alarm on the battlefield
• Thraben Doomsayer on the battlefield
• Thraben Doomsayer does not have summoning sickness

Steps

1. Activate Thraben Doomsayer by tapping it, creating a 1/1 Human token
2. Human token enters the battlefield, triggering Intruder Alarm, untapping all creatures
3. Repeat

Results

• Infinite creature tokens
• Infinite ETB