Lucy’s skeleton costume may have been a Day of the Dead reference. It works out-of-universe as a nod to the actress’ heritage and in-universe for its significance to the cursed personalities
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On a sillier note, the costume (complete with paper bag mask) could also refer to the mostly-headless Australopithecus skeleton known as Lucy.
And here I thought it might be a nod to The Paper Bag Princess, a book by Robert Munsch 😀
I mean, Ivy could have put a balaclava on the kid instead, probably easier for Lucy to see in than through the paper bag slits, and if black would look way cooler, more like a headless skeleton 🙂 But I suppose they’d only have a balaclava if they were skiers, or lived somewhere colder than Seattle.