Wikipedia classifies this as a "dark fantasy" film, although the book it's based on is referred to as "horror-fantasy children's ..." - the latter strikes me as more accurate.
The main character is Alex, a young boy who loves to write scary stories. But on his birthday, his best friend abandons him because he's too weird. Alex is heartbroken, and leaves his apartment to burn his "Nightbooks" (all the stories he's written) in the building's boiler room. But on the way he's lured into an apartment by "Lost Boys" on the TV and a piece of pumpkin pie. Where he becomes trapped, and finds himself required to create a new scary story every night for an evil witch (Krysten Ritter). He meets a young woman named Yazmin (Lidya Jewett) also trapped and enslaved, and a hairless magical cat called Lenore. Yazmin and Alex plot to escape.
In classic children's horror style, Ritter's witch is garish, absurd, and not terribly bright (they have to outsmart her). She is at least mildly menacing as she can and does kill children that she's unhappy with. Yazmin and Alex are cute, and make the movie almost worth watching. I was underwhelmed - but then, I'm an adult watching a kids' "horror" movie.