While you control Necrovalley and a Gravekeeper, creatures your opponents control get -1/-1.

{1}{B}{B}{B/G}, {T}: take one Necrovalley from your hand or graveyard and put it onto the battlefield. You can only activate this ability if you control no other enchantments and at least two Gravekeepers.

When Necrovalley Temple enters the graveyard after leaving the battlefield, you may pay {2}{B}{B}. If you do, search your library for a card with Necrovalley in its name, reveal it, put it into your hand, then shuffle your library.