Call to the Grave

Symmetry with a built-in escape hatch for whoever cast it: the enchantment grinds the board down one creature per upkeep, but Zombies are exempt, so the obvious shell is a Zombie deck that watches everyone else's army feed the saw while its own stays untouched. That tribal carve-out is the whole engine. It turns a draining global sacrifice effect into a one-sided board-clear for the player who showed up with the right creature type, and it does the work at the start of each upkeep rather than as a one-time wrath, so it keeps eating the next thing the opponent commits. The self-sacrifice clause on the end step is the cost of leaving it pointed only at others: strip the board down to nothing and the enchantment goes too, which keeps it from becoming a permanent prison once the Zombies are also gone. As a piece of Onslaught-block tribal design it reads as a black answer to the question of how to make a creature type matter beyond its lords and combat tricks, by punishing every deck that isn't built around it. The catch is timing and patience: it gives each player the choice of which creature to lose, so opponents shed their worst bodies first, and the effect rewards a board state already tilted toward your Zombies rather than creating that advantage from a standing start.