Mikaeus, the Unhallowed, Putrid Goblin, and Altar of Dementia

Prerequisites

• Mikaeus, the Unhallowed on the battlefield
• Putrid Goblin on the battlefield
• Altar of Dementia on the battlefield

Steps

1. Activate Altar of Dementia by sacrificing Putrid Goblin
2. Putrid Goblin dies, triggering its persist and undying abilities
3. Resolve the persist trigger, returning it from your graveyard to the battlefield with a -1/-1 counter on it
4. Resolve the undying trigger, doing nothing
5. Resolve the Altar of Dementia ability, causing target player to mill cards equal to Putrid Goblin's power
6. Activate Altar of Dementia by sacrificing Putrid Goblin
7. Putrid Goblin dies, triggering its undying ability, returning it from your graveyard to the battlefield with a +1/+1 counter on it
8. Resolve the Altar of Dementia ability, causing target player to mill cards equal to Putrid Goblin's power
9. Activate Altar of Dementia by sacrificing Putrid Goblin
10. Putrid Goblin dies, triggering its persist ability, returning it from your graveyard to the battlefield with a -1/-1 counter on it
11. Repeat from step 5

Results

• Infinite +1/+1 counters on Altar of Dementia
• Infinite death triggers
• Infinite ETB
• Infinite LTB
• Infinite sacrifice triggers