Casey Jones, Back Alley Brute, and Phyrexian Devourer

Prerequisites

• Casey Jones, Back Alley Brute on the battlefield
• Phyrexian Devourer on the battlefield

Steps

1. Activate Phyrexian Devourer by exiling the top card of your library, putting a number of +1/+1 counters on it equal to the exiled card's mana value
2. Casey's second ability triggers, and Phyrexian Devourer triggers if it's power is 7 or greater
3. Resolve the Casey trigger, dealing damage to an opponent
4. Holding priority, repeat from step 1 until your library
5. Resolve all Phyrexian Devourer triggers, sacrificing it

Results

• Exile your library
• Near-infinite damage