This loop is brilliantly orchestrated by Leyline of Transformation, which turns every creature you control into a Cleric right from the start of the game. That type reassignment is the crucial missing link, allowing any ordinary creature you sacrifice to Viscera Seer to satisfy Rotlung Reanimator's death trigger. Every time you feed a creature to the Seer, the Reanimator steps in to replace it with a fresh 2/2 Zombie token, which itself enters as a Cleric ready to be sacrificed again. This creates a closed-loop engine for infinite sacrifices, leaves, and entries, all while Viscera Seer lets you sculpt the top of your library indefinitely until you dig up the exact win condition you need.