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 Murderous Redcap by paying {2}{B/R}{B/R}.
When Murderous Redcap enters the battlefield, it and Warden of the Grove trigger.
Resolve the Warden of the Grove trigger, putting a +1/+1 counter on Murderous Redcap.
Resolve the Murderous Redcap trigger, dealing an amount of damage to itself equal to its power.
Murderous Redcap dies as a state-based action due to having 0 toughness.
Murderous Redcap's persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
Repeat from step 2.

Infinite LTB

Infinite death triggers

Murderous Redcap

Activate Skirk Prospector by sacrificing Scuzzback Marauders, adding {R}.
When Scuzzback Marauders dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
When Scuzzback Marauders enters the battlefield, Warden of the Grove triggers, putting a +1/+1 counter on Scuzzback Marauders
Repeat.

Infinite sacrifice triggers

Infinite red mana

Skirk Prospector

Scuzzback Marauders

Activate Skirk Prospector by sacrificing Putrid Goblin, adding {R}.
When Putrid Goblin dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
When Putrid Goblin enters the battlefield, Warden of the Grove triggers, putting a +1/+1 counter on Putrid Goblin.
Repeat.

Putrid Goblin

Cast Dargo from the command zone by paying {R}.
When Dargo enters the battlefield, Warden of the Grove triggers, putting a +1/+1 counter on Dargo.
Activate Dargo using Wild Cantor's ability by sacrificing it, adding {R}.
Choose to return Dargo from your graveyard to the command zone.
Repeat.

Infinite storm count

Infinite commander casts

Dargo, the Shipwrecker

Wild Cantor

Activate Yidaro's cycling ability by paying {1}{R} and discarding it.
Yidaro triggers, putting it from your graveyard onto the battlefield.
When Yidaro enters the battlefield, Warden of the Grove triggers, putting a +1/+1 counter on Yidaro.
Resolve the Yidaro cycling ability, causing you to draw a card.
Activate Yidaro using Grinning Ignus's ability by paying {1} and returning Yidaro from the battlefield to your hand, adding {C}{C}{R}.
Repeat.

Combos with "Warden of the Grove"