Neerdiv, Devious Diver, Agatha's Soul Cauldron, and Aphetto Alchemist

Prerequisites

• Neerdiv, Devious Diver on the battlefield
• Agatha's Soul Cauldron on the battlefield
• Aphetto Alchemist in exile

Steps

1. Activate Neerdiv using Aphetto Alchemist's ability by tapping it
2. Neerdiv triggers, causing a player to mill cards equal to its power
3. Resolve the Neerdiv ability from step 1, untapping it
4. Repeat

Results

• Infinite mill
• Infinite self-mill