Mortuary + Grinding Station + Bolas's Citadel + Shield Sphere

Mortuary

Grinding Station

Bolas's Citadel

Shield Sphere

How it works

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

This clever loop transforms free artifacts into an endless engine, fueled by Bolas's Citadel allowing you to cast cards directly from the top of your library using your life total instead of mana. By tapping Grinding Station to sacrifice Shield Sphere, you send the zero-mana defender straight to the graveyard, where Mortuary instantly intercepts it to place it right back on top of your library. Whenever Shield Sphere re-enters the battlefield, Grinding Station's triggered ability untaps the mill artifact so you can repeat the process indefinitely, milling out your opponents while generating a storm of creature sacrifices and enters-the-battlefield triggers.