Altar of the Lost

Mana that can only do one thing is a strange currency, and this is one of the few rocks to mint it deliberately. The two mana it taps for is the cleanest fixing in the game: any colors, no restriction on which, which would be obscene on a normal artifact. The catch is the spend clause. It pays only for flashback, and only from the graveyard, so the value of the second tap is exactly as high as the number of flashback cards you have stocked and no higher. Outside that narrow lane the mana evaporates. What that buys, when the graveyard is full, is a deck that effectively plays two spells off one card and pays for the back half with an artifact that produces colors it has no business producing. The entering-tapped clause is the only speed tax on an otherwise free engine, a one-turn delay against fixing that warps how cheaply a graveyard-flashback shell can splash a third or fourth color. It is a piece of build-around design that does nothing in a vacuum and a great deal in the one deck constructed to abuse it: the rare mana source whose ceiling is set entirely by the contents of your own graveyard.