Agatha's Soul Cauldron + Grist, the Hunger Tide + Bloodspore Thrinax

Agatha's Soul Cauldron

Grist, the Hunger Tide

Bloodspore Thrinax

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. The Insect enters the battlefield with a +1/+1 counter on it due to Bloodspore Thrinax, causing it to have Grist's abilities.
3. Repeat from step 1 using the Insect token instead.

This intricate loop begins by using Agatha's Soul Cauldron to exile Grist, the Hunger Tide from a graveyard, granting its activated loyalty abilities to your creatures that bear +1/+1 counters. When Bloodspore Thrinax enters the battlefield with its devour ability, it ensures that subsequent creatures—fueled by the Cauldron's color-fixing mana—enter with the necessary +1/+1 counters to immediately inherit Grist's abilities. With these pieces aligned, you can repeatedly activate Grist's first ability via the token to generate infinite creature tokens, trigger infinite creature ETBs, and self-mill your entire library.