Is the jam only for new games or work in progress can be an entry too?

I have a game prototype where I could add a boss fight, for example.

I'm afraid not, as this would give an unfair advantage to anyone who had a project ready to go, or even halfway developed. If the project was very early in development, then it could be OK, but as stated in the jam page, roughly at least 3/4 of the game should be made in jam time.

ok thanks :)