Obviously many other factors are added here, such as the centering of the print on the paper, front and back (yes, how well the design is positioned on the piece of cardboard), the quality of the holographic foil, and other parameters of which I have never had the courage to deepen knowledge
As for the extra deck, I would take out 1 of the Maestrokes and add in Utopia Ray, since you're already running Utopia, and a few more generic rank 4's, like Abyss Dweller, Photon Pap, Gagaga Cowboy, Daigusto Emeral, and Gem Knight Pearl
Like most Pokmon cards, the value of Furfrou depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Perfect Order)
The name was likely changed to avoid the religious connotations associated with demons
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