Games should be made entirely within the time period - I would look for comparable public assets or make something new. That said, if the assets are simple enough, it seems fair to reuse them as long as you make them available to the public.
Ok yeah sounds fair. As a follow-up question: are the songs ludwig plays on his streams/videos also fair game as long as its not DMCA/TOS? (like other game OSTs, Mariya Takeuchi, reddit recap theme, etc.)
I have a generic first person character controller that I use for a lot of my games, would it be okay to use that, and then post the Unity Asset online for others to download if they wish?
