Cauldron of Souls, Corridor Monitor, Cathars' Crusade, and Altar of Dementia

Prerequisites

• Cauldron of Souls on the battlefield
• Corridor Monitor on the battlefield
• Cathars' Crusade on the battlefield
• Altar of Dementia on the battlefield
• Corridor Monitor does not have a -1/-1 counter on it

Steps

1. Activate Cauldron of Souls by tapping it, giving Corridor Monitor persist until end of turn
2. Activate Altar of Dementia by sacrificing Corridor Monitor
3. When Corridor Monitor dies, its persist ability triggers, returning itself from your graveyard to the battlefield with a -1/-1 counter on it
4. When Corridor Monitor enters the battlefield, it and Cathars' Crusade trigger
5. Resolve the Corridor Monitor trigger, untapping Cauldron of Souls
6. Resolve the Cathars' Crusade trigger, putting a +1/+1 counter on each creature you control
7. Resolve the Altar of Dementia ability from step 2, causing target player to mill cards equal to Corridor Monitor's power
8. Repeat

Results

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