Priest of Gix

Cast it for three mana, get three black back, and the ledger reads zero: this is mana filtering wearing a 2/1 body, not acceleration. The trick is the conversion. Two of those three returned pips can come from generic-flavored sources, but what comes out is strictly black, exactly the currency that heavy single-color costs and devotion counts crave. Where Dark Ritual burns a card to net mana and then is gone, this leaves a creature in play, and that residue gives the card its second life. The enters trigger only breaks even on cast, so its value is not the first appearance but every appearance after. Any blink, bounce, or reanimation effect fires the trigger again for another three black, and once you pair it with a free sacrifice outlet that recurs it from the graveyard, the body's death stops being a cost. The loop wants it dead: Ashnod's Altar eats the creature to produce mana, a recursion piece returns it, and the enters trigger hands you three black on the way back. Survival never enters into it; the engines that exploit this design are happiest grinding it through the yard on repeat. As a one-shot it is forgettable, a creature you cast for free and ignore. As the recurring half of a black-mana loop, it quietly supplies the fixed output that keeps the math closing every cycle.