Prowling Geistcatcher + Phyrexian Delver + Gray Merchant of Asphodel + Umbral Collar Zealot

Prowling Geistcatcher

Phyrexian Delver

Gray Merchant of Asphodel

Umbral Collar Zealot

How it works

1. Activate Umbral Collar Zealot twice by sacrificing Phyrexian Delver and Gray Merchant.
2. When Phyrexian Delver and Gray Merchant die, Prowling Geistcatcher's first ability triggers twice, exiling Phyrexian Delver and Gray Merchant from your graveyard.
3. Activate Umbral Collar Zealot by sacrificing Prowling Geistcatcher.
4. When Prowling Geistcatcher dies, its second ability triggers, returning Phyrexian Delver and Gray Merchant from exile to the battlefield.
5. When Phyrexian Delver and Gray Merchant enter the battlefield, they trigger.
6. Resolve the Gray Merchant trigger, causing each opponent to lose an amount of life equal to your devotion to black, and causing you to gain life equal to the life lost this way.
7. Resolve the Phyrexian Delver trigger, causing you to return Prowling Geistcatcher from your graveyard to the battlefield and lose 4 life.
8. Resolve the Umbral Collar Zealot abilities from steps 1 and 3.
9. Repeat.

This elegant loop hinges on Prowling Geistcatcher acting as a safe haven, temporarily exiling your fallen creatures rather than letting them linger in the graveyard. By feeding both Gray Merchant of Asphodel and a previous sacrifice to Umbral Collar Zealot, you fuel your initial deaths before finally sacrificing the Geistcatcher itself. Its departure triggers the return of everything it held, allowing Phyrexian Delver to enter and immediately resurrect the Geistcatcher while Gray Merchant drains your opponents dry.