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

Mortuary

Blasting Station

Bolas's Citadel

Shield Sphere

How it works

1. Activate Blasting 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 Blasting Station ability.
4. Cast Shield Sphere from the top of your library by paying 0 life.
5. When Shield Sphere enters, Blasting Station triggers, untapping Blasting Station.
6. Repeat.

This infinite loop relies on a clever zero-cost recycling system centered around Shield Sphere, which can be repeatedly sacrificed to Blasting Station to deal damage and then instantly recast thanks to the top-deck manipulation of Mortuary. Because Shield Sphere has a mana value of zero, Bolas's Citadel allows you to play it right off the top of your library without paying any life at all. Meanwhile, every time the tiny artifact re-enters the battlefield, Blasting Station triggers to untap itself, setting the stage to sacrifice it all over again.