Agatha's Soul Cauldron + Grist, the Hunger Tide + Warden of the Grove

Agatha's Soul Cauldron

Grist, the Hunger Tide

Warden of the Grove

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, Warden of the Grove 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.