The trailer for the slasher movie was released as the cartoon character entered the public domain.
It's Mickey, but not as you've ever seen him before.
A trailer for a slasher film, featuring a masked killer dressed as Mickey Mouse, was released on 1 January, the day that Disney's copyright on the earliest versions of the cartoon character expired in the US.
"We wanted the polar opposite of what exists," the movie's producer said.
A new Mickey-inspired horror game, showing the rodent covered with blood stains, also dropped on the same day.
Steamboat Willie, a 1928 short film featuring early non-speaking versions of Mickey and Minnie, entered the public domain in the US on New Year's Day.
It means cartoonists, novelists and filmmakers can now rework and use the earliest versions of Mickey and Minnie.
Note that Mickey Mouse himself is most definitely trademarked and protected via IP laws. The
mouse himself may still also be copyrighted (I haven’t bothered to look)
Creating derivative works is still most certainly illegal.
tl;dr you can freely share Steamboat Willie, but you should not try to create your own Mickey Mouse shows since Disney has no issue bankrupting you in a copyright/trademark lawsuit.
They can use the character, as long as they don't advertise in a way that infringes on Disney's trademark (can't use the mouse silhouette etc.) and they can only use the character as he appeared in the 1928 short, he can't have gloves or red shorts like the Mickey we know now does.
It's a tightrope, but it's possible to use the character legally. I'm sure Disney's lawyers are looking over this stuff with a magnifying glass though.