Weakstone

Defensive global combat math, sold as a colorless artifact. The design move is small and underrated: instead of buffing your blockers (which fails against trample, evasion, and unblocked damage), the card shaves a point off every attacker, so it scales linearly with how wide the opposing board goes and lands its full value before blocks are even declared. That distinction matters. A Glorious Anthem-style pump on defense answers one creature at a time; a static minus to attackers answers the whole red zone at once, and it punishes go-wide strategies harder than it punishes a single fatty. The cost is the era's accepted price for a colorless permanent effect with no activation, no upkeep, no sacrifice clause: you pay four up front and the discount runs forever. The lineage from here runs through Meekstone, Crawlspace, and Ensnaring Bridge: artifacts that tax combat rather than remove creatures, sold to decks (mono-color, artifact-prison, colorless ramp) that needed a defensive tool their color pie did not provide. The companion piece, Mightstone, gives attackers +1/+0 and was designed as the deliberate inverse; the two were later fused into Urza's lore as halves of the same machine, which is the flavor beat the card is best remembered for now.