Mortuary + Shilgengar, Sire of Famine + Bolas's Citadel + Ornithopter

Mortuary

Shilgengar, Sire of Famine

Bolas's Citadel

Ornithopter

How it works

1. Activate Shilgengar by sacrificing Ornithopter
2. When Ornithopter dies, Mortuary triggers, putting Ornithopter from your graveyard onto the top of your library.
3. Resolve the Shilgengar ability.
4. Cast Ornithopter from the top of your library by paying 0 life.
5. Repeat.

This loop transforms Shilgengar, Sire of Famine into an engine of endless tribute by using Mortuary as a magical sorting mechanism whenever a creature dies. When you sacrifice Ornithopter to Shilgengar, Mortuary immediately catches it on its way to the graveyard and places it right back on top of your library. That positioning is vital because Bolas's Citadel allows you to play the Ornithopter directly from the top of your library for zero life, priming it to be sacrificed to Shilgengar once more.