What exactly does Necrovalley negate and what passes thru it? I know it's all in the wording, but being into magic for a while now, wording rules are different between games.

If a card targets, or specifically designates, a card in the graveyard outside of itself, Necrovalley will cause it to fail. Examples are Premature Burial, Chaos Sorceror's special summon, or Kycoo's special effect. If a card does not specifically designate a card in the graveyard besides itself, Necrovalley does nothing. Examples are Sangan and Treeborn Frog.