Mortuary + Viscera Seer + Phyrexian Walker + Bolas's Citadel

Mortuary

Viscera Seer

Phyrexian Walker

Bolas's Citadel

How it works

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

This elegant loop transforms the ultimate artifact engine of Bolas's Citadel into a bottomless well of sacrifice and death triggers by letting you cast spells directly from the top of your library. When you use Viscera Seer to sacrifice the free artifact creature Phyrexian Walker, Mortuary catches it on its way to the graveyard and immediately places it right back onto the top of your library. Thanks to Bolas's Citadel allowing you to play spells straight from your library's apex—paying a mana value of zero life for Phyrexian Walker—you can repeat this cycle indefinitely without ever running out of resources.