Thresher Beast

The block-and-sacrifice clause hands the entire combat decision to the defender, and that is the whole trick: stop this 4/4 with a creature and you lose a land of your choice; let it through and you keep your mana base while taking four. The design question being poked at was how to make a midsize green beater threaten something beyond raw damage, and the answer here was the opponent's lands rather than their life total. The problem is that the trigger never forces itself: a defender who simply declines to block takes the four and keeps every land intact, so the threat depends entirely on someone choosing to chump. That makes it a clock that warps decisions rather than one that demands them, daring the opponent to trade a permanent for the privilege of stopping a swing. It works as land destruction smuggled into the combat step: no spell to cast, no permanent to target, just a body that turns blocking into an expensive proposition. Among green's early experiments in pressuring resources instead of life, it reads as a curiosity, an attempt to make the attack itself the source of disruption, undercut by the fact that the disruption only ever happens if the other player agrees to it.