Untaidake, the Cloud Keeper

The price is the constraint: two life every time you tap it, and two colorless that flows nowhere except into legendary spells. That second restriction is the entire bargain. The land exists to power the dragons, the named warlords, and the legendary spirits of a design era built around legendary permanents, and it does nothing for the rest of your deck. Entering tapped already concedes a turn of tempo; the life payment concedes the rest. What you get back is a meaningful chunk of acceleration toward a top-end that is, by definition, splashy and singular. The lineage here runs through every land that has tried to ramp a specific class of spell rather than ramp generally: the design idea is that a land which only feeds one archetype can be pushed harder than one that feeds everything, because the keyhole caps the abuse. The trouble has always been that "only legendary spells" is a narrower opening than it first looks, and the cards it pays for have to be worth bleeding for. When they are (a fast, expensive legend you want a turn early), this is exactly the enabler it was drawn to be. When they aren't, it's a land that taps for nothing and asks you to pay for the privilege.