Al-abara's Carpet

Ten mana on the turn you want it: that is the real cost of this activated fog, the kind of arithmetic Magic stopped asking players to do almost immediately. Five to cast, five more and a tap to fire, and what you buy is prevention scoped to a single narrow dimension of combat: ground attackers hitting the controller specifically. Planeswalkers, players other than you, damage from non-attacking creatures, anything with flying: all uncovered. The artifact stays on the battlefield to do it again next turn, if you can find the mana again, which is the whole conceit of an early repeatable prevention engine.

The pricing reads as punitive, and it is, but it survives from the stretch of design where Wizards was still feeling out how cheap a recurring prevention effect could be without warping things. The answer, eventually, was that even at this rate the design was uncomfortable enough that the lineage mostly died off. Maze of Ith solved the ground-attacker problem on a land at no recurring mana cost; Moat solved it as a static lock against non-fliers. The activated-artifact-fog branch was quietly pruned in favor of those cleaner answers. What remains here is the texture of an older design philosophy, one where a five-mana artifact could legitimately cost five more to fire and still earn a slot in a deck built to plan its turns around it.