Rakdos, the Muscle + Priest of Gix + Haunted Crossroads + Spawning Pit + Cloud Key

Rakdos, the Muscle

Priest of Gix

Haunted Crossroads

Spawning Pit

Cloud Key

How it works

1. Activate Spawning Pit 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 Spawning Pit 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 loop relies on a clever mana-reduction engine where Cloud Key, set to creatures, discounts Priest of Gix so that its own entry-trigger provides more black mana than it costs to recast. By feeding the Priest to Spawning Pit, you generate a charge counter and send the creature to the graveyard, where Haunted Crossroads lets you tuck it back onto the top of your library for a single black mana. Rakdos, the Muscle catches the sacrifice by exiling those top cards of your library with permission to play them, letting you churn through your entire deck while continuously turning a profit of mana, triggers, and counters.