Prowling Geistcatcher, Kiki-Jiki, Mirror Breaker, and Altar of Dementia

Prerequisites

• Prowling Geistcatcher on the battlefield
• Kiki-Jiki, Mirror Breaker on the battlefield
• Altar of Dementia on the battlefield

Steps

1. Activate Kiki-Jiki by tapping it, creating a token copy of Prowling Geistcatcher with haste
2. Activate Altar of Dementia by sacrificing Kiki-Jiki
3. When Kiki-Jiki dies, the nontoken and token Prowling Geistcatcher's first abilities trigger
4. Resolve the token Prowling Geistcatcher's trigger, exiling Kiki-Jiki from your graveyard
5. Resolve the nontoken Prowling Geistcatcher's trigger, doing nothing
6. Resolve the Altar of Dementia ability, causing target player to mill cards equal to Kiki-Jiki's power
7. Activate Altar of Dementia by sacrificing the Prowling Geistcatcher token
8. When the token Prowling Geistcatcher dies, its second ability and the nontoken Prowling Geistcatcher's first ability triggers
9. Resolve the nontoken Prowling Geistcatcher trigger, putting a +1/+1 counter on it
10. Resolve the token Prowling Geistcatcher trigger, returning Kiki-Jiki from exile to the battlefield
11. Resolve the Altar of Dementia ability, causing target player to mill cards equal to the token Prowling Geistcatcher's power
12. Repeat

Results

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