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

Agatha's Soul Cauldron

Grist, the Hunger Tide

Master Biomancer

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 Master Biomancer, causing it to have Grist's abilities.
3. Repeat from step 1 using the Insect token instead.

This brilliant loop turns your graveyard and library into an engine for infinite value, anchored by Agatha's Soul Cauldron exiling Grist, the Hunger Tide so its activated ability becomes available to your board. Master Biomancer ensures that any new tokens entering the battlefield arrive with a +1/+1 counter already on them, allowing them to instantly inherit Grist's abilities through Agatha's Soul Cauldron's static text. This lets the newly minted creature immediately activate Grist's +1 ability to create more tokens, mill your deck, and potentially trigger itself again if you hit an Insect.