Ob Nixilis, Captive Kingpin, Agatha's Soul Cauldron, and Walking Ballista

Prerequisites

• Ob Nixilis, Captive Kingpin on the battlefield
• Agatha's Soul Cauldron on the battlefield
• Walking Ballista in exile
• Ob Nixilis has at least one +1/+1 counter on it

Steps

1. Activate Ob Nixilis using Walking Ballista's second ability by removing a +1/+1 counter from it, dealing 1 damage to an opponent
2. Ob Nixilis triggers, putting a +1/+1 counter on itself and exiling the top card of your library
3. Repeat

Results

• Exile your library
• Infinite damage