Arcum's Weathervane

Two activated abilities, one to add the snow designation and one to strip it, make this an artifact built to do exactly one thing: police a supertype. The set that introduced it leaned on snow as a counting resource, with effects that scaled off how many snow permanents you controlled, and a mechanic that lives or dies by board state invites a tool that can edit that state on either side. Toggle an opponent's land off snow to cut their payoffs, or convert your own basics on to feed them. The trouble is that snow was never load-bearing enough to need this kind of enforcement, so the Weathervane was a solution sized for a problem that stayed theoretical. Its real interest is conceptual: an early, almost literal attempt to treat a supertype as a contested resource, something you could attack and defend rather than merely accumulate. Wizards would return to snow much later with a cleaner mana-based payoff structure, but this card is the seam where the idea first showed: a supertype-manipulation answer in a metagame that never produced the synergies worth answering.