Not joining but I thought it would be helpful for those joining who dont have an idea of what to make, the nI got some suggestions: (FYI: Got no idea if these are any good or what the optional theme is)

- A clicker game that changes the music by how many of each unit you have or by how much you are earning per second

- A platformer that adapt to how you play (if you go fast the music speeds up)

- A choose your own adventure game that adapts the music by how kind your choices are to those you meet

If you got any ideas yourself but are not joining or got something else you want to do please share them, I would love to read what people come up with.