Activate only if both a "Gravekeeper's" monster and "Necrovalley" are on the field. Neither player can Special Summon monsters, except "Gravekeeper's" monsters. If either a "Gravekeeper's" monster or "Necrovalley" is not on the field, destroy this card.
The effect of this card that forbid players to special summon is very powerful. However, not easy to keep this spell card on the field since Necrovalley field spell is not available in Duel Links. You have to have Gravekeeper's Priestess that has effect treating the field as Necrovalley.