I'm wondering if there is a word for a non-funny spoof/parody, as described in the title.
Without giving away any spoilers, Invincible (the TV series, haven't read the comics) seems very much like an alternative reality/mashup of classic super heros (the parallels are obvious, Superman, Gambit, Flash, Batman etc) but told in a very dark way.
Like a dark homage?
A word that might fit is to call such a work a reimagining. A reimagining of a work takes existing elements like characters, setting, genre, tropes, or plot, and changes them in some way. It doesn't necessarily indicate that the new work is darker or grittier or not comical, but a reimagined work will often differ in key aspects like plot or tone. Typically, a reimagining will subvert certain elements of the original work in some way.
In the example you mention, the work could be described as a reimagining of common superhero tropes.
Juvenalian Satire
Juvenalian satire, in literature, any bitter and ironic criticism of contemporary persons and institutions that is filled with personal invective, angry moral indignation, and pessimism. The name alludes to the Latin satirist Juvenal, who, in the 1st century ad, brilliantly denounced Roman society, the rich and powerful, and the discomforts and dangers of city life. Samuel Johnson modeled his poem London on Juvenal’s third satire and The Vanity of Human Wishes on the 10th. Gulliver’s Travels (1726) established Jonathan Swift as the master of Juvenalian satire. In the 20th century, Karl Kraus’s indictments of the prevailing corruption in post-World War I Austria were in the Juvenalian tradition.
[emphasis mine]
If anger is your energy—for instance, if you wanted to subvert the status quo and attack the venality of the political class or religious leaders—then Juvenalian satire is your best bet. Freed from the shackles of being outright funny, the mission of Juvenalian satire is often to attack individuals, governments and organisations to expose hypocrisy and moral transgressions. For this reason, writers should expect to use stronger doses of irony and sarcasm in this concoction.
I don't know that there's a word for that, a word that means what "spoof" means but replaces the part that makes it definitively satirical with definitively "dark" or "gritty."
"Adaptation" (see def. 3 with example) is the neutral word, the word for "spoof" that doesn't expressly denote that the work is a parody, is satirical, so lacking any other word that means "dark adaptation," "gritty adaptation," or "dark, gritty adaptation," you would say "adaptation" with those adjectives, or whatever adjectives you intend, beforehand to describe it (e.g., The 1999 film Cruel Intentions is an modernized adaptation of the 1988 period film Dangerous Liaisons, which itself is a screenplay adaptation of Pierre Choderlos de Laclos' 1782 novel Les Liaisons dangereuses).
By the way, there's even the film Adaptation, which is very meta in that it's an adaptation of a short story the movie's author, Charlie Kauffman, had previously written about himself trying to write an adaptation of the 1998 nonfiction book The Orchid Thief.
You quote Invincible as an example, and that is firmly in the genre of superhero deconstruction, along with other works such as The Boys and Watchmen.
Quoting the relevant page on the TV Tropes wiki:
"Deconstruction" literally means "to take something apart". When applied to tropes or other aspects of fiction, deconstruction means to take apart a trope in a way that exposes its inherent contradictions, often by exploring the difference between how the trope appears in this one work and how it compares to other relevant tropes or ideas both in fiction and Real Life.
A pastiche is one word that fits:
a piece of art, music, literature, etc. that intentionally copies the style of someone else's work or is intentionally in various styles, or the practice of making art in either of these ways. Source
A pastiche isn't necessarily gritty and dark but it can be.
It could be a reinterpretation of a theme, an idea, or probably more concretely also a story.
The entry at Merriam-Webster's gives the example "the director wants to reinterpret the old play for a modern audience", which seems to fit your use case nicely.
In The Art of Fiction, John Gardner called this, “high parodic form (the way Shakespeare seriously parodied the revenge tragedy in Hamlet, for example)”. (Emphasis added.)
Another example he gives is when he brainstorms the idea of trying to tell a “tale” of Helen of Troy today:
Though on reflection we may understand Homer’s method and reconstruct the ancient mindset, I think we must say that we simply cannot think like that. To revive the epic, the modern writer must commit himself to irony and a detached, self-conscious objectivity foreign to the original epic style. He cannot write an epic but only an earnest parody that works chiefly as a study of the artistic mind or as a comment on art by art. Perhaps this parodic revival of the genre might work for the writer who has chosen to treat the Helen story as a fictional exploration of Life versus Art, but if the writer’s theme is private and community values, the revival of epic form seems fruitless.
He speaks more highly of how Edgar Allen Poe does it:
The imitations I've mentioned [...] are all fairly sophisticated; that is, far removed from the base of imitation. Much closer following of the model can achieve equally interesting—and new—results. Many of Poe's stories are imitations or parodic comments. His “Imp of the Perverse,” for instance, imitates the style of Washington Irving and attacks the philistinism and anti-intellectualism of Irving’s “Legend of Sleepy Hollow.” Though we sometimes associate parody with college humor magazines or such popular organs as Mad magazine and the National Lampoon, the use of parodic technique, both comic and serious, has proved a rich vein for contemporary writers. (It has been a mainstay of poets for centuries.)
In my experience, the most common name for a dark version of some media, especially fantasy or science fiction, especially film, is the gritty reboot.
This is the term used by Know Your Meme and Urban Dictionary, the latter of which defines it as
Re-starting a film franchise from the very beginning and making it a grittier, more realistic version that will appeal to adults.
This term is used widely; a web search for the term immediately brings up numerous articles discussing merit or lack thereof for given reboots, or for the very concept, or even for the very term itself. GQ magazine ran an article on the history of these reboots.
This term is fairly recent—the Know Your Meme article points to 2009 for its coinage. I suspect that it’s somewhat unlikely to stand the test of time—right now, gritty reboots are very much “in,” having exploded into popularity most notably with Batman Begins. They’re new, they’re hot, Hollywood is obsessed with them. But audiences may already be tiring of them—and in the case of at least some choices, ridiculing them. The GQ article, for example, was prompted by the announcement of a gritty reboot for The Powerpuff Girls, which as the name might suggest, is not a property particularly ripe for this treatment. (Then again, I have heard good things about the gritty reboot of Sabrina the Teenage Witch, a choice I had found about as surprising, so who knows?)
The point is, sooner or later, there will likely be a backlash against over-gritty rebooting, and we’ll see less of them done, and then at some point thereafter, it will be “safe” to make them on occasion, hopefully reserved for a particularly deserving re-imagining. It’s not clear that we’ll still be calling them “gritty reboots” at that point, though. If they become less common—particularly if there’s a distinct lull in which few if any are made for a while—we may no longer have a term for them and then if they come back as a cultural force, we may well coin another term for them. After all, as the GQ article discusses, the concept of a gritty reboot considerably predates the term “gritty reboot.”
