Rakdos, the Muscle + Priest of Gix + Haunted Crossroads + Umbral Collar Zealot + Temur Battlecrier

Rakdos, the Muscle

Priest of Gix

Haunted Crossroads

Umbral Collar Zealot

Temur Battlecrier

How it works

1. Activate Umbral Collar Zealot by sacrificing Priest of Gix.
2. When Priest of Gix dies, Rakdos triggers.
3. Holding priority, activate Haunted Crossroads by paying , putting Priest of Gix from your graveyard onto the top of your library.
4. Resolve the Rakdos trigger, causing you to exile the top three cards of your library with the ability to play them until your next end step.
5. Resolve the Umbral Collar Zealot ability from step 1.
6. Cast Priest of Gix from exile by paying at most 2.
7. When Priest of Gix enters the battlefield, it triggers, adding .
8. Repeat.

This ingenious loop centers around Rakdos, the Muscle, whose sacrifice trigger lets you exile and subsequently play cards from your library. By sacrificing Priest of Gix to Umbral Collar Zealot, you generate a stream of black mana and death triggers while setting up your next draw with a surveil. Haunted Crossroads then lets you loop the Priest right back to the top of your library for a single black mana, ensuring it is ready to be cast from exile. While the engine runs independently, Temur Battlecrier even stands ready to discount those casting costs if your board develops the requisite power.