Zombie sounds too limiting to me. A popular character in any form of spooky costume could do for Halloween, but spooky, scary, and mythical are already demonstrated by a large number of cards that a special gift card wouldn't stand out. Noel cards stand out because until Brampah, there wasn't any Chrismas-y cards besides them.
I would also like to state that holiday-wise they've already released something fitting. Uchtul. He was given to those who worked really hard for him, like how getting the most candy on Halloween requires a lot of running around, but soon after Halloween, everyone will be able to get him for a price, like how candy and costume prices DROP come Nov. (To continue this metaphor, Noels are given to everyone on Chrismas because that's what people do during that holiday, they give.)
Actually thats a good idea "Spooky" in front of the card name, that way it can be any costume; like you said vampire, zombie, doesn't matter. So "Spooky Beeboy" that has a nicer ring to it.
As for Uchtul, I guess you could count that as a Holiday type event.....but if you read the comments close, they said that other clans after Nightmare may also be getting a card in the same fashion; so it leads me to believe that this wasn't a generic Halloween holiday type event.
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