the pitch for Fantasy High is essentially what it says on the tin - a fantasy story about adventurers who learn how to Adventure at an academy in a town modelled after America in the 50's (though it's quickly kind of discarded beyond some aesthetics bc the characters take out phones and have internet), and uses a lot of tropes from like 80's American high school movies like the Breakfast Club and all. thematically it's a lot about how the main "Bad Kids'" relationships with each other, other students, and their families, finding themselves and questioning themselves, and so forth.
understandably, while it's part of the joke to have "wizard classes" and such (as in classes taught by a wizard, not the wizard class explicitly), dnd 5e... does not work with this premise. like at all. listen i've been that person, i've tried to run school-settings for dnd before, it is so clunky and just doesn't fit with what you're doing. i mean hell, wizards of the coast tried it too with strixhaven and they bungled that real bad to the point where i usually hear people refer to it as "the first system agnostic module produced by wotc because no system works with it"! 5e already barely works, and a fantasy war game for your quirky high school campaign is just so awkward.
so what ttrpg system do i think they should've used? Masks: A New Generation, a PbtA game about young superheroes. yeah, maybe it's hypocritical to suggest using a superhero game for a fantasy setting, but let's be real, a lot of superhero powers are basically magic, and wouldn't giving the characters individual abilities provide a more interesting take on what magic is in the world for brennan's worldbuilding, rather than sticking with dnd's uninspired magic system? the influence system could work so well with the story, like imagine Kristen getting to break the influence her parents have on her in the first season and changing playbooks after that, and Fabian would've fit perfectly as the Legacy, imo. i guess if they were incredibly attached to being fantasy "classes" and all, i guess they could make some kind of combination of dungeon world and masks? but i think Masks best represents what kind of story they really wanted to make, personally.
do i really need to say it? City of Mist. The Unsleeping City should've used City of Mist. City of Mist is basically what the concept of Unsleeping City sets out to be. the characters are even solving mysteries in the game. it should've been a City of Mist game. not goddamn dnd 5e in modern day New Yawk. come on man.
i don't know if i'm fully against using a more tactical war game for horror settings, i think it's probably possible to do it well, but in the end dnd and games of its ilk are generally, inescapably, about murdering strangers and beasts in your path for treasure and being very heroic about it, preferably emerging victorious. the kind of horror story Neverafter at least presents itself as is one about transformation and feeling like you have no control of your own story and trying to wrestle that control back. mind, i haven't seen the full season because i have very little money and can't pay for dropout tv, so i can't give a full analysis on what the show could use, but my first - and very predictable - thought is Heart - The City Beneath by Grant Howitt and Christopher Taylor.
Heart is a darling game that i adore a lot personally, and i think it does very interesting things with the horror fantasy setting it has. some of the classes are very specific to the setting that Heart presents, which Friends at the Table had to change a little to make it work with their own setting of Sangfielle, so i think the cast and crew of Dimension 20 - which have far more writers and budget than Friends at the Table have - could take the time needed to make Heart work with the Neverafter setting. which wouldn't be much, i imagine! Rosamund, the Sleeping Beauty character, could be a Deep Apiarist flavored to have thorns rather than Bees And Bugs in her body, for example, and the Red Riding Hood character could be a Cleaver, etc etc
Now, maybe the general idea of Heart - of playing characters that will inevitably lose themselves to the titular "Heart" - doesn't quite fit with the kind of story they ended up telling, since i believe it ends with a happily ever after type ending, but... that doesn't feel much like horror to me. if you're setting out to do a horror season, stick to it, you know? not that horror never has happier endings or anything, but, you know, characters should be changed in ways that are often for the worse after all they endure, and frankly, i would rather see a story that breaks from the usual mold of something that leaves you with a fuzzy feeling of knowing it was All Okay In The End. Heart, instead, works on the premise that the Zenith of your abilities are one where you do something very powerful... and then you either die or are irreversibly transformed and lost forever. this does not Have to be the fate of your character by the end of the campaign, a Heart campaign doesn't have to end with all your characters using their zenith abilities one by one, but i think it would be more interesting than all of the characters managing to wrestle control of their stories. i would like to see some fail. i would like to see some of them do worse things, when they do take control of their stories.
so yeah i think Heart would be a good fit. maybe Spire would suit better if they really wanted to stick with building towards an ending where everyone manages to take control of their own lives and their own narratives, even if Spire isn't exactly a much happier game than Heart.
i hate star wars 5th edition i hate it with my life. play a different game for the love of god. ahem. anyways. so here i actually have three suggestions rather than just one. the ones i'd suggest are Star Wars FFG (Edge of the Empire and Force And Destiny), Stars Without Number, and finally, Scum And Villainy.
Star Wars FFG is, quite plainly, mostly here because they used a star wars overhaul of dnd 5e more than anything, though i am personally enchanted by FFG narrative dice and i think the system itself is pretty neat. Stars Without Number is a choice that i don't know if it would fully fit their style given the mortality rate of characters in OSR games, but there are rules for heroic characters in SWN that would suit them much better i feel, and hey, one of the characters in Starstruck Odyssey is a psychic fish alien who has to stay in water and uses robot bodies to interact with the surface world, and SWN has rules for having "Shells", synthetic bodies that a consciousness can be placed in, even accounting for an AI or transhumanist character having multiple synthetic bodies that they would use for different occasions! crazy how some systems have like rules and stuff, huh.
finally, Scum And Villainy is a Forged in the Dark system (based on Blades in the Dark's rule system) that takes inspiration from things such as Star Wars and Cowboy Bebop, where players play as either smugglers, bounty hunters, or rebels, deciding what kind of crew they are during shared character creation. for all of the issues i have with dimension 20, the cast is an entertaining bunch, and i can imagine that a fitd system would fit their playstyle fairly well if they were properly introduced to it. it's easy enough to map each of the characters to the seven available playbooks, too, i think, and Scum And Villainy's a good time as someone who's GMed it myself, and it's easy to make things chaotic (complimentary) which this cast seems to enjoy. Scum And Villainy would be my personal pick but that's in part because i just enjoy fitd games so much