Mystic Decree

The World enchantment supertype is the load-bearing piece here, and it's the part the oracle text doesn't explain. Only one World permanent can exist at a time: a new one entering forces the older to the graveyard, which turns this from a static hatebar into a contested slot anyone can overwrite. That mechanic frames what the card actually is: a blanket revocation of two evasion abilities, aimed squarely at the flying and islandwalk that defined so much of early-game combat math. Stripping flying off the board flattens an entire axis of attacking and blocking, and erasing islandwalk neuters the unblockable-against-blue plan that the era leaned on heavily. The catch is that it cuts both ways and respects no allegiance; your own fliers come down to earth alongside the opponent's, so the card rewards a creature base built on the ground rather than around it. As a symmetric, removable lock it sits in a strange design pocket: powerful enough to reshape combat, fragile enough that a second World enchantment ends it, and indiscriminate enough that you have to want the symmetry. It is a relic of a moment when flying was the premier evasion keyword and Wizards was still experimenting with World permanents as a self-limiting answer to board states, a supertype the design team would eventually stop printing precisely because the "only one exists" rule created more confusion than the effects justified.