Necrovalley and Graveyard-Protection Floodgates

Some Field Spells and continuous effects protect the Graveyard by preventing and negating effects that touch GY cards. The canonical case is Necrovalley. This is a different mechanic from a banish-instead replacement (Macro Cosmos, Dimensional Fissure; see Send-to-GY Costs Under Banish-Instead Effects) — a replacement silently redirects a destination, whereas Necrovalley either makes a cost impossible to pay or lets the effect activate and then negates it. Don't conflate the two: they give opposite activatability answers.

Verbatim text

Necrovalley — "All 'Gravekeeper's' monsters gain 500 ATK and DEF. Cards in the Graveyard cannot be banished. Negate any card effect that would move a card in the Graveyard to a different place. Negate any card effect that changes Types or Attributes in the Graveyard."

Four separate clauses: (1) a Gravekeeper's ATK/DEF buff, (2) a prevention — GY cards cannot be banished, (3) a negation — effects that would move a GY card to another place are negated, (4) a negation of effects that change a GY card's Type/Attribute.

The load-bearing distinction: cost vs. effect

Whether a card can even be activated under Necrovalley turns on whether the GY interaction is a cost or part of the resolution:

• Cost that banishes / moves a card from the GY → cannot be activated at all. The cost cannot be paid because Necrovalley prevents the banish, so the activation is illegal from the start. Examples: Spore, Prophecy Destroyer, Blaster, Dragon Ruler of Infernos (its first/banish-cost effect) — all banish from the GY as a cost, so none can be activated while Necrovalley is face-up.
• Effect (at resolution) that moves/banishes a GY card → CAN be activated, but is negated. You may activate it normally; when it resolves, Necrovalley negates the part that would move the GY card. Examples: Monster Reborn, Pot of Avarice, D.D. Crow (its banish is its effect, not a cost) — all activatable, all negated by Necrovalley.

This mirrors the cost-vs-effect axis in Targeting and Cost vs. Effect and the banish-instead rule: a cost that the floodgate makes impossible blocks the activation; an effect that the floodgate negates still activates and then does nothing for that part.

Worked examples

"Can I activate Monster Reborn targeting a monster in my GY while Necrovalley is on the field?"

— Answer: Yes, you can activate it — but Necrovalley negates it. Reviving the GY monster "moves a card in the Graveyard to a different place," so Necrovalley's third clause negates the effect at resolution; the monster stays in the GY and Monster Reborn is sent to the GY having done nothing. (Contrast the cost cases below, which cannot even be activated.)

"Can I activate Spore (banish 1 Plant from my GY) while Necrovalley is up?"

— Answer: No. Spore's self-Special-Summon requires banishing a Plant from the GY as a cost, and "Cards in the Graveyard cannot be banished," so the cost cannot be paid — the activation is illegal. Same for Prophecy Destroyer and Blaster's banish-cost effect.

"D.D. Crow targeting a card in my opponent's GY, under Necrovalley?"

— Answer: Activatable, but negated. D.D. Crow banishes the GY card as its effect (not a cost), so you can activate it; Necrovalley then negates the banish at resolution. (An older write-up said D.D. Crow "can't be activated at all" — that is outdated; the current ruling is activate-then-negate, because the banish is an effect, not a cost.)

Generalized principle

For any "GY cannot be [acted on]" / "negate effects that touch the GY" floodgate:

1. Find whether the blocked GY action is a cost (before the `;`) or an effect (resolution). Cost → unactivatable; effect → activatable but negated.
2. A prevention ("cannot be banished") and a negation ("negate any effect that would move…") both stop the value, but only the cost version blocks activation.
3. Self-contained effects whose only purpose is the negated action still resolve doing nothing — they are not "illegal to activate" unless the blocked action was their cost.

Keep this separate from a banish-instead replacement (file 21), which never negates — it just changes the destination, and only blocks activation when a cost specifically names the now-unavailable GY destination.

Judge calls to watch for

• Necrovalley prevents GY banishing and negates effects that move/retype GY cards — it does not "send those cards somewhere" or destroy them.
• Cost to banish/move from the GY → cannot activate (Spore, Prophecy Destroyer, Blaster first effect). Effect that moves a GY card → can activate, gets negated (Monster Reborn, Pot of Avarice, D.D. Crow). Decide by reading whether the GY action is before or after the `;`.
• Do not rule that every GY-touching card "cannot be activated" under Necrovalley — only the cost-based ones. Effect-based ones activate and are negated.
• This is a prevent/negate floodgate, not a banish-instead replacement (file 21). Opposite activatability: a replacement only blocks a cost that names the GY destination; Necrovalley blocks any cost that banishes from the GY and negates resolution-time GY moves.
• The Gravekeeper's +500 ATK/DEF clause applies to "Gravekeeper's" monsters including ones turned into monsters by other effects.