i think the most impactful one is easily neverending story. there's apparently a lot more interwoven with the book - red/green duality, narrator figures, et cetera - but i think the movie itself also does a great job of conveying the things i think are the important parts of late homestuck. the post-gameover wasteland of the alpha session is so evocative of fantasia after it's been destroyed by the nothing, and the scene where bastian reads a description of atreyu, sees the horse pin on his bag, and decides atreyu is an indigenous character, bringing in the context of his lived experience into the story, really hits in the context of the ways people tend to play like, paper doll dressup with homestuck characters.

it's hugely influential on the way i think about the relationship between reader and text, not because those ideas weren't already there, but because the way they manifest in the neverending story is so clear in homestuck as well.