Chaosphere

Combat in Magic has a default hierarchy that nobody talks about because it never moves: fliers block fliers and ground creatures, ground creatures block only the ground, and that one-way permeability is what makes flying the cleanest evasion keyword in the game. This rewrites the rule at the root. The two clauses pull in opposite directions: ground creatures gain reach and can suddenly wall off the air, while fliers lose the ability to block anything that isn't airborne, stripping them of their defensive value in the same breath. It reads as a symmetrical chaos effect, but it almost never lands symmetrically, because the deck running it has built a ground force that no longer fears the skies while the opponent's aerial plan collapses into a row of overpriced bodies that can't even defend. The reach grant is the more elegant half of the templating. Rather than deleting flying as a keyword, it answers the keyword by elevating everything else to meet it, which is a tidier solution than the blunter "creatures lose flying" effects that show up elsewhere; flying still does what it says, it just no longer means anything. That it is a World enchantment is a holdover from an early supertype that lets only one World permanent exist at a time across the table, a rules artifact more than a balance lever, since a global combat-rewrite like this is sweeping by its nature.