Sepulchral Primordial + Infinite Reflection + Yahenni, Undying Partisan

Prerequisites

• You have a way to cause a nontoken creature to enter the battlefield under your control.
• An opponent has a creature card in their graveyard.

Steps

1. 1Cause a nontoken creature to enter the battlefield under your control, which enters as a copy of Sepulchral Primordial due to Infinite Reflection.
2. 2When the creature enters, it triggers. Holding priority, activate Yahenni by sacrificing the creature.
3. 3Resolve 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. 4Repeat from step 2.

Effects

• Infinite creature ETB
• Infinite creature LTB
• Infinite creature sacrifice triggers
• Infinite death triggers