Agatha's Soul Cauldron + Grist, the Hunger Tide + Arwen, Weaver of Hope
Infinite ETB, Infinite self-mill, Infinite creature tokens
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.
The Insect enters the battlefield with a +1/+1 counter on it due to Arwen, causing it to have Grist's abilities.
Repeat from step 1 using the Insect token instead.
Component Cards
How It Works
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.
The Insect enters the battlefield with a +1/+1 counter on it due to Arwen, causing it to have Grist's abilities.
Repeat from step 1 using the Insect token instead.