Holding priority, cast Naru Meha by paying its mana cost.
When Naru Meha enters, it triggers, copying Graceful Reprieve, with the copy targeting Naru Meha.
Resolve the copy of Graceful Reprieve.
Holding priority, activate Shilgengar by sacrificing Naru Meha.
When Naru Meha dies, Graceful Reprieve triggers, returning Naru Meha from your graveyard to the battlefield.
Repeat from step 3.
Resolve all Shilgengar abilities from step 5.
This clever loop begins by casting Graceful Reprieve, followed immediately by Naru Meha, Master Wizard so that its enter-the-battlefield ability can target the spell on the stack with a copy. When Naru Meha is then sacrificed to Shilgengar, Sire of Famine, the original Graceful Reprieve resolves and immediately returns the Wizard to the battlefield, setting up an endless cycle of enters-the-battlefield and death triggers. Along the way, Shilgengar's sacrifice ability happily turns every iteration into a steady stream of Blood tokens, while Naru Meha ensures the recursion never stops.