Agatha's Soul Cauldron, Grist, the Hunger Tide, and Master Biomancer

Prerequisites

• Agatha's Soul Cauldron on the battlefield
• Grist, the Hunger Tide in exile
• Master Biomancer on the battlefield
• Master Biomancer has at least one +1/+1 counter on it

Steps

1. Activate Master Biomancer using Grist's first loyalty ability by putting a loyalty counter on it, causing you to create a 1/1 Insect creature token and mill a card, and then put a loyalty counter on Master Biomancer and repeat the process if the card was an Insect
2. The Insect enters the battlefield with at least three +1/+1 counters on it due to Master Biomancer, causing it to have Grist's abilities
3. Repeat from step 1 using the Insect token instead

Results

• Infinite creature tokens
• Infinite ETB
• Infinite self-mill