Weirdly I feel like level 9 is harder than level 10 or 11. Next will be level 12, and if I can find it... level 13
Since this game is so old it's also rather difficult to find. There are ISO's out there. Ballance was running at 1800 FPS when I first reinstalled it on Windows 10, meaning I had to download MSI After Burner and use the Rivatuner tool to limit the FPS to 60 so the game could run correctly.
