Agatha's Soul Cauldron + Grist, the Hunger Tide + Good-Fortune Unicorn

Agatha's Soul Cauldron

Grist, the Hunger Tide

Good-Fortune Unicorn

How it works

1. Activate a creature 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, Good-Fortune Unicorn triggers, putting a +1/+1 counter on the Insect. This causes it to gain Grist's abilities due to Agatha's Soul Cauldron.
3. Repeat from step 1 using the Insect token instead.

This clever loop harnesses Agatha's Soul Cauldron to turn your creatures into planeswalkers, feeding an infinite chain of creation. By exiling Grist, the Hunger Tide with the Cauldron, its loyalty abilities become activated abilities available to your creatures that bear +1/+1 counters. Good-Fortune Unicorn ensures that every time a new token enters the battlefield, it immediately receives a +1/+1 counter—giving it the necessary access to Grist's abilities and allowing the newly spawned Insect to continue the mill and token-generation process indefinitely.