Say she's out, nobody has a copy of Necrovalley anywhere, and, long story short, there's no way anyone in the area of that Duel has any way of confirming what Necrovalley's effects are.
My question at this point is this: How can you prove what its effects that she's supposedly conveying to the field are?
Simple answer: You can't. Reciting it from memory won't work, since your opponent can easily claim you're making it up or wrong (which you may very well be).
Besides, the effect comes from the card itself, not the field being treated that way. Necrovalley doesn't give a 500 ATK/DEF boost to Gravekeepers because the field's treated as Necrovalley, it gives them that because the Field Spell Card has an effect that does it. The Field Spell Card, not what the field's treated as. The card's effect and what the field is treated as are separate things.
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