Mikaeus, the Unhallowed, Soulstinger, and Altar of Dementia

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Soulstinger on the battlefield
• Altar of Dementia on the battlefield
• Soulstinger does not have a +1/+1 counter on it

Steps

1. Activate Altar of Dementia by sacrificing Soulstinger
2. When Soulstinger dies, its second and undying abilities trigger
3. Resolve the first trigger, allowing you to put a number of -1/-1 counters on a creature equal to the number that were on Soulstinger
4. Resolve the undying trigger, returning it from your graveyard to the battlefield with a +1/+1 counter on it
5. When Soulstinger enters the battlefield, its first ability triggers, putting two -1/-1 counters on it
6. Resolve the Altar of Dementia ability, causing target player to mill cards equal to Soulstinger's power
7. Repeat

Results

• Infinite -1/-1 counters
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite mill
• Infinite sacrifice triggers
• Infinite self-mill