Prowling Geistcatcher, Saffi Eriksdotter, and Altar of Dementia

Prerequisites

• Prowling Geistcatcher on the battlefield
• Saffi Eriksdotter on the battlefield
• Altar of Dementia on the battlefield

Steps

1. Activate Saffi by sacrificing it, targeting Prowling Geistcatcher
2. When Saffi dies, Prowling Geistcatcher's first ability triggers, exiling Saffi from your graveyard
3. Resolve the Saffi ability
4. Activate Altar of Dementia by sacrificing Prowling Geistcatcher
5. When Prowling Geistcatcher dies, its second ability and Saffi trigger
6. Resolve the Saffi trigger, returning Prowling Geistcatcher from your graveyard to the battlefield
7. Resolve the Prowling Geistcatcher trigger, returning Saffi from exile to the battlefield
8. Resolve the Altar of Dementia ability, causing target player to mill cards equal to Prowling Geistcatcher's power
9. Repeat

Results

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