Not be confused with Pops the Slayer Man (https://www.imdb.com/title/tt33362807/), also coming out next year.
The main benefit that public domain brings to a work is that you can make small edits or changes to a work without violating its copyright. Imagine if you wanted to go through all the episodes of Spongebob, change the colors to make it clearer to watch for colorblind viewers[a], and then sell those edits as a box set or otherwise sell access to them via some accessibility-focused streaming service. Under copyright this would probably not be seen as transformative, and something non-transformative then has an incredibly high bar to clear for fair use to apply to it.
I also think that making new episodes that aren't super transformative would probably not have met the burden for Fair use: for example, making a new episode of Popeye that otherwise follows the same script beats as existing episodes would probably be seen as copyright infringement by the courts. However, once you get into the territory of making a sequel/prequel movie where you really flesh out his character, it starts getting into the realm of qualifying for transformative under fair use (depending on how the judge sees it).
But the mentioned movies really seem like they're so different from the source material. For Pooh Blood and Honey, it doesn't affecting the market for the original, given the works are so different in what they do (and there is likely 0.1% or less overlap between the audience of the slasher genre and the children's programming genre cohort), it did not use almost any of the original copyrighted works to tell its story, just its characters, and the content is transformative enough to where it's not like it's just another episode of Winnie The Pooh.
This popeye film seems to use the same approach as Blood and Honey: it's just Popeye killing people with stuff like "look, it's the Spinach from the original episodes!".
a: not sure if this would actually be beneficial, but it's the best example I can think of for a barely-transformative work other than putting sunglasses on the characters' faces or putting Subway Surfers next to it.
It's less that "what counts as fair use" is ambiguous because litigation is expensive, and more that each situation of reuse is unique to where the law has codified that fair use be determined on a case-by-case basis. Case law can aid in proving your case for fair use, but there is not a framework for quashing a challenge to your fair use if your case is basically a carbon-copy of an existing legal case.
Even in this reality, for something like Pooh Blood and Honey, Disney wouldn't have touched it since their every action in legal proceedings (especially copyright-related ones) is closely followed by enthusiasts, bloggers, and the mainstream media alike. If Disney had challenged the Pooh slasher film while he was copyrighted it probably would've grossed an extra 10 million dollars.
For a movie that could be a video player that applies certain effects and transformations at the right timestamps.
~~I think that parody would be a far better defense than fair use.~~ But I otherwise agree that those gore movies based on children cartoons would probably be legal even before the original works had become public domain. At most, they might've required a tiny misspelling to be 100% legal and safe to sell.
I mean, South Park already had a gore parody of Mickey Mouse[1] decades before Steamboat Willie went public domain. In fact, South Park's Mickey Mouse has traits from later movies, still copyrighted in 2024, like the eye shapes and the lack of a tail.
That's why I'm unimpressed by these low quality gore parodies. What's actually going to be more exciting are the sincere animated adaptations that could be made from public domain stories, like del Toro's Pinocchio.
My favourite: https://en.wikipedia.org/wiki/The_Adventures_of_Tintin:_Brea...
Others: https://en.wikipedia.org/wiki/List_of_Tintin_parodies_and_pa...