This clever loop hinges on the unique interplay between Isilu, Carrier of Twilight and Melira's Keepers, where Isilu grants persist to your nontoken creatures while Melira's Keepers relies on its static ability to prevent -1/-1 counters from ever being placed upon it. Because Melira's Keepers ignores these counters entirely, its persist trigger brings it straight back to the battlefield cleanly every single time it dies. You can repeatedly feed this resilient creature to Yahenni, Undying Partisan's sacrifice ability to gain endless sacrifice, death, and entry triggers. Meanwhile, the front face of that same permanent, Eirdu, Carrier of Dawn, provides the broader framework with convoke to help you cast your spells, though this specific engine runs entirely on the relentless cycle of sacrifice and resurrection.