Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight, and Altar of Dementia

Prerequisites

• Eirdu, Carrier of Dawn // Isilu, Carrier of Twilight on the battlefield
• Altar of Dementia on the battlefield

Steps

1. Activate Altar of Dementia by sacrificing the undying creature
2. When the creature dies, its undying ability triggers, returning the creature from your graveyard to the battlefield with a +1/+1 counter on it
3. Activate Altar of Dementia by sacrificing the undying creature
4. When the creature dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it
5. Resolve the Altar of Dementia abilities from step 1 and 3
6. Repeat

Results

• Infinite LTB
• Infinite ETB
• Infinite sacrifice triggers
• Infinite death triggers
• Infinite mill
• Infinite self-mill