Sheoldred, Whispering One

Two engines that pull in opposite directions, fused onto one seven-mana body, and the asymmetry is the whole point. The upkeep recursion only ever serves you: every turn the graveyard refills the board with a creature, no payment beyond having one to bring back. The sacrifice clause only ever taxes them: each opponent's upkeep strips a creature away, edict-style, dodging hexproof and protection because the choice is theirs but the loss is not. The result is a clock that widens the board on one side and erodes it on the other, every single round it survives. The recursion target is any creature in your yard, so the card pairs naturally with creatures that earn their second death, the ones with enters-the-battlefield triggers or end-step sacrifice outlets that turn the loop into an engine rather than a single reanimation. Swampwalk reads as a vestigial flavor nod (a Phyrexian crawling through the muck of a corrupted plane) but it does mean the body is often unblockable against black decks, a small mercy on a creature already built to grind.

What separates this Praetor from the reanimation spells that came before is that it does not cast one big threat and hope; it institutionalizes the engine. The danger is the runaway: leave it untouched a single turn cycle and the symmetry collapses entirely, your side compounding while theirs hollows out. Removing it is the only real answer, which is exactly the bind a seven-mana late-game wall is designed to create.