Activate Shilgengar by sacrificing Archon of Falling Stars.
When Archon of Falling Stars dies, it triggers, returning Necromancy from your graveyard to the battlefield.
When Necromancy enters the battlefield, it triggers, returning Archon of Falling Stars from your graveyard to the battlefield, and attaching Necromancy to it.
Resolve the Shilgengar ability.
Repeat.
This haunting resurrection loop is fueled by Shilgengar, Sire of Famine, whose ability lets you sacrifice your own creatures to generate Blood tokens. When you sacrifice Archon of Falling Stars to that cost, its death trigger fires to pull Necromancy straight out of your graveyard and back to the battlefield. The moment Necromancy enters, its own trigger targets that very same Archon of Falling Stars in your graveyard, returning it to the battlefield and attaching itself as an Aura. This creates a perpetual engine of sacrifices and returns, letting you churn out infinite Blood tokens while cycling your creatures through death and resurrection endlessly.