Help! Ending!

The story at the end turns the killer into a real life ghost/hallucination, which causes the writer to freak out.  In his freaky stage he runs off and falls down stairs/gets run over in traffic/jumps off a balcony, that kind of thing.  Then the typewriter types that event by itself, finishing with "The End."

So... no one can help me?

The ending you seek is in John Carpenter's 'In the Mouth of Madness', just watch it and rip off the ending. Your teacher will never know!

^
Yeah, that works too, uless it's  Umberto Lenzi's Nightmare City and ... the dream... is becoming a reality!!! Nooo, spare us Umberto!

Or you can pull Fulci's "The Beyond" ending when reality blurs at the end.

Orrrrrrrrrrrrrrrrrrrrrrrr you could just do it yourself.

DIY at it's finest.

What a revolutionary idea!

But seriously though you should stick with the cat ending. It will be a shocking twist because no one ever suspects the innocent cat.

Don't listen to Tripod, he's leading you up the garden path with his silly idea about cats.

Everyone knows that dogs are well more shady and sinister. End it with a doberman mauling the cat authors throat. Write in a quick scene about the dog mauling someone's leg and you can call it Do Slay Knee.

I guess a small "twist" of In The Mouth Of Madness: The guy wrote out so many fictional and dangerous criminals that the world went into post-apocalyptic. He got ill pretty bad and must stay in hospital for 3 years while still writing his stories with the typewriter while also being tormented by some semi-real characters surrounding his room. When he went ( and before that, he oreders some people to throw the typewriter away.) out of the hospital the world was, like I've said before... post-apocalyptic and probably also dystopian type. He wonders around a book store and find a book very big (HUUUGE!) book called : "From Adam Clark's Madness." and go to read it only to find that it ultimately re-tell his actions since when he find the machine and find a huge collection of numerous of his crime fiction stories. He was narrated in the first person so he's gonna spend the rest of his life reading that huge book and write the whole story (this story) in an apartment.