Mortuary + Phyrexian Altar + Bolas's Citadel + Kobolds of Kher Keep

Mortuary

Phyrexian Altar

Bolas's Citadel

Kobolds of Kher Keep

How it works

1. Activate Phyrexian Altar by sacrificing Kobolds of Kher Keep
2. When Kobolds of Kher Keep dies, Mortuary triggers, putting Kobolds of Kher Keep from your graveyard onto the top of your library.
3. Cast Kobolds of Kher Keep from the top of your library by paying 0 life.
4. Repeat.

This clever loop centers around the free sacrifice outlet Phyrexian Altar, which converts our creatures directly into any color of mana. To make this endless, we use Kobolds of Kher Keep as our recurring fuel since its zero mana value lets Bolas's Citadel cast it straight from the library for zero life. Meanwhile, Mortuary intercepts the Kobolds every time they hit the graveyard, neatly stacking them right back onto the top of our library to be cast all over again.