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.
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.
Repeat from step 1 using the Insect token instead.

Infinite ETB

Infinite self-mill

Infinite creature tokens

Agatha's Soul Cauldron

Grist, the Hunger Tide

Warden of the Grove

Cast Doomsday by paying {B}{B}{B}, choosing any five Insects in your graveyard and/or library, exiling the rest of your library and graveyard, then putting the Insects into your library in any order.
Cast Wheel of Sun and Moon by paying {G/W}{G/W}, attaching it to yourself.
Activate Grist's first loyalty ability by putting a loyalty counter on it, causing you to create a 1/1 Insect creature token, put a loyalty counter on Grist and mill a card.
The card is instead revealed and put on the bottom of your library due to Wheel of Sun and Moon.
Repeat the process, causing you to create a 1/1 Insect creature token, put a loyalty counter on Grist and mill a card.
Because this process will repeat infinitely, the game ends in a draw.

Draw the game

Doomsday

Wheel of Sun and Moon

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 Thunderous Velocipede, causing it to have Grist's abilities.
Repeat from step 1 using the Insect token instead.

Combos with "Grist, the Hunger Tide"