"Necrovalley" (ネクロバレー Nekurobarē) is an archetype based around the Field Spell of the same name and is best used with the "Gravekeeper's" archetype. They focus on controlling the field and limiting the options of your opponent by preventing them from using their Graveyard as a resource, banishing cards in the Graveyard, denying Special Summoning of non-"Gravekeeper's" monsters, and negating effects that activate on the field.
"Necrovalley" was introduced in Pharaonic Guardian, with "Hidden Temples of Necrovalley" and "Imperial Tombs of Necrovalley" being introduced in Legacy of the Valiant. While "Necrovalley" works as a stand-alone Field Spell, "Hidden Temples" and "Imperial Tombs" require the player to control "Necrovalley" itself and at least 1 "Gravekeeper's" monster. The same set also introduced "Gravekeeper's Ambusher" as support for this archetype.