Archon of Falling Stars and Yahenni on the battlefield.
Steps
Activate Yahenni 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 Yahenni ability, giving it indestructible until end of turn.