Mountain Valley

Part of the Mirage fetch cycle, the design that fixed two colors at the literal cost of a card and a turn of tempo before "pay a life" became the genre's standard currency. The entry-tapped clause is the whole balancing act: the search itself is unconditional, but you front-load the cost by losing a turn of mana before the land can ever crack. That makes it slower than the Onslaught and Zendikar fetches that came later, the ones that traded a point of life for the privilege of grabbing land untapped on the turn they hit the table. What it gives up in speed it returns in scope: because it pulls any Mountain or Forest card rather than only a basic, it can thin toward dual lands and nonbasics that carry those types, a flexibility the streamlined modern fetches inherited but never expanded on. The sacrifice clause also means the land removes itself from the battlefield as part of the search, the same shuffle-and-thin logic every fetchland since has run on. This is the rough draft of an idea Magic refined for a decade: the fixing is real, the deck-thinning is real, and the cost is paid in time rather than blood.