Mortuary + Grinding Station + Bolas's Citadel + Ornithopter

Mortuary

Grinding Station

Bolas's Citadel

Ornithopter

How it works

1. Activate Grinding Station by tapping it and sacrificing Ornithopter
2. When Ornithopter dies, Mortuary triggers, putting Ornithopter from your graveyard onto the top of your library.
3. Resolve the Grinding Station ability.
4. Cast Ornithopter from the top of your library by paying 0 life.
5. When Ornithopter enters, Grinding Station triggers, untapping Grinding Station.
6. Repeat.

This looping engine turns free artifacts into an endless mechanical heartbeat by turning graveyard recursion directly into library manipulation. With Bolas's Citadel letting you cast spells directly off the top of your library for a mere pittance of life instead of mana, you can deploy Ornithopter over and over again without ever running out of resources. Each time that little flyer hits the battlefield, Grinding Station untaps itself so you can sacrifice the Ornithopter right back to its own activation cost. As the Ornithopter heads to the graveyard, Mortuary instantly catches it and places it right back onto the top of your library, perfectly positioned for Bolas's Citadel to play it again while Grinding Station mills your opponents out entirely.