Marble Priest

An artifact creature that rewrites how Walls interact with combat, built for an era when Walls were the dominant defensive primitive and "creatures that can't attack hold the ground" was the entire shape of the archetype. The compulsion clause is the interesting half. Forcing every able Wall to block flips the Wall's role from passive ground stop to mandatory blocker, which turns the opponent's defensive investment into a liability they cannot opt out of. The damage prevention then ensures the trade is one-sided: the Priest swings into the Walls, the Priest takes nothing, and the opposing board of defenders feeds itself into a 3/3 over successive turns. Functionally this is a hoser, narrowly aimed at a metagame Legends expected to exist and that largely did, where Wall of Stone, Wall of Wood, and their cousins were how decks bought time against early creatures. The rate is poor by any modern standard, and the targeting is so specific that the card simply does nothing when the opponent has no Walls. That specificity is the design point, not a flaw: this is a sideboard-shaped main-deck card from before sideboards were a stable concept, built to punish a single archetype and to be unremarkable against everything else.