Sepulchral Primordial + Infinite Reflection + Umbral Collar Zealot

Sepulchral Primordial

Infinite Reflection

Umbral Collar Zealot

How it works

1. Cause a nontoken creature to enter the battlefield under your control, which enters as a copy of Sepulchral Primordial due to Infinite Reflection.
2. When the creature enters, it triggers. Holding priority, activate Umbral Collar Zealot by sacrificing the creature.
3. Resolve the creature's trigger, putting a creature card from an opponent's graveyard onto the battlefield under your control as a copy of Sepulchral Primordial.
4. Repeat from step 2.

This clever loop turns graveyard thievery into an engine by letting you repeatedly trigger Sepulchral Primordial's entry ability. While Infinite Reflection ensures every new creature enters the battlefield as a copy of the Primordial, Umbral Collar Zealot provides the crucial sacrifice outlet that cleans away the current copy and feeds your graveyard with surveil triggers. By sacrificing the Primordial-copy in response to its own trigger, you continuously raid your opponents' graveyards for fresh threats while generating infinite entry, death, and sacrifice triggers.