Colfenor, the Last Yew, Gutter Grime, Hangarback Walker, and Altar of Dementia

Prerequisites

• Colfenor, the Last Yew on the battlefield
• Gutter Grime on the battlefield
• Hangarback Walker in hand
• Altar of Dementia on the battlefield

Steps

1. Cast Hangarback Walker by paying
2. Hangarback Walker enters the battlefield and dies as a state-based action due to having zero toughness
3. Gutter Grime triggers, putting a slime counter on it and creating a X/X Ooze creature token
4. Activate Altar of Dementia by sacrificing the Ooze
5. When the Ooze dies, Colfenor triggers, returning Hangarback Walker from your graveyard to the battlefield
6. Resolve the Altar of Dementia ability, causing target player to mill cards equal to the Ooze's power
7. Repeat

Results

• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite mill
• Infinite sacrifice triggers
• Infinite self-mill
• Infinite storm count
• Infinite slime counters on Gutter Grime