Playroom - Okay, so there are two cuts of this movie on YouTube. I watched the shorter one, but there's a longer version (like a minute or so longer) showing a downer ending that is available in international cuts of the film. I'd heard about this before I sat down to watch it and I was sure I had guessed it. 

The actual ending: the survivor, Jenny, is locked up in an institution for the murders of the other characters (pretty sure I've been over how and why I hate this trope).

My guess: ...well, at one point, Jenny and archaeologist Chris have sex (in the underground tomb; your guess is as good as mine as to why) and it's established that Chris is slowly being influenced by the evil Prince Ilok (and at one point, he states that he can never leave the tomb), so what if no protection was used and Jenny has been knocked up with a possible reincarnation of Ilok inside of her?

If I was the type that leaned toward unhappy endings, I would probably try to have one of my scripts end like this.