Hidden Necropolis

A tapped mono-black source that eventually eats itself for a Discover 4 is doing something quietly unusual: it collapses a manabase slot and a spell slot into one card, spending the early game producing black and the late game converting itself into a free cast without ever costing you a card in hand. While it sits, the land is inert value; the sacrifice clause turns those idle turns into a payoff, casting the first nonland hit for free or banking it. The math is deliberately gated. The activation runs five mana () plus the tap and the sacrifice of the land itself, and the sorcery-speed clause locks the whole thing to your main phase. All of that pays for what would otherwise be an aggressively cheap way to turn a land into gas. Discover's cap at mana value four keeps the pull honest: this is not a Genesis Wave that scoops the whole deck, it is a curve-topper that respects the low end of a deck built to abuse free casts. The tension in the design is between wanting a land and wanting a spell, and this refuses to make you choose at deckbuilding: it is a land right up until the moment you decide it is not. The entering-tapped clause is the tax that stops that flexibility from being free, a small speed cost charged up front against a card that otherwise asks nothing extra of your list.