Tolarian Academy

The most banned land in the game's history, and the one that taught Wizards what a land that scales with the rest of your deck actually costs. The trap is that the mana scales explosively while the spells that build the artifact count cost nothing in the era it was printed: an early-era flood of free and near-free artifacts (Mana Vault, the moxen, accelerants of every shape) meant a single tap could pour out enough blue to chain a turn most decks could not survive. That is the structural flaw the rate hides. A normal land caps at one mana; this one's ceiling is set by how many artifacts you can deploy before it untaps, which is to say there is no ceiling. The legendary supertype is the card's only brake, and it brakes nothing: you only ever needed one. It headlined the Combo Winter that broke format after format in turn, and it remains restricted or banned in essentially every format that has ever had to reckon with it. As a design object it is the cautionary tale Wizards cites internally whenever a land is asked to do more than produce one mana: the lesson that a land scaling off another resource in your deck does not add a little power, it removes the cost ceiling entirely.