"Halloween" is a super rough guideline because we didn't want to restrict people to just "Horror" or "Ghost" or anything like that. You can theme the levels with halloween themed creatures and assets, for example, or just have the main character as a ghost. Pretty much anything you yourself consider to be Halloween-themed can work. Also there's a rule which says the game doesn't have to be horror and that we want to encourage people to be creative, so I have a feeling that the majority of the games won't be horror. Hopefully this helped and good luck on your game!