Agatha's Soul Cauldron, Cathars' Crusade, and Grist, the Hunger Tide

Prerequisites

• Agatha's Soul Cauldron on the battlefield
• Cathars' Crusade on the battlefield
• Grist, the Hunger Tide in exile
• You control a creature with a +1/+1 counter on it

Steps

1. Activate a creature you control 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 the creature and repeat the process if the card was an Insect
2. When the Insect enters the battlefield, Cathars' Crusade triggers, putting a +1/+1 counter on each creature you control and causing the Insect token to gain Grist's abilities
3. Repeat from step 1 using the Insect token instead

Results

• Infinite +1/+1 counters
• Infinite creature tokens
• Infinite ETB
• Infinite self-mill