Agatha's Soul Cauldron + Grist, the Hunger Tide + Combine Guildmage

Agatha's Soul Cauldron

Grist, the Hunger Tide

Combine Guildmage

How it works

1. Activate Combine Guildmage's first ability by paying 1 and tapping it.
2. 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.
3. The Insect enters the battlefield with a +1/+1 counter on it due to Combine Guildmage, causing it to have Grist's abilities.
4. Repeat from step 2 using the Insect token instead.