I'm not entirely sure if this is the correct forum for this, but I have a slight problem with J1CS. I can't figure out how to make a level with no "sun tile." Does anyone know how to do this? I'd rather not have an ugly black square following me through the level.

Uncheck the Sun checkbox in "Level Properties". If you don't have that, you have an outdated version of J1CS.

Thanks, I've got the better version now.

I have a new problem, though. Whenever I try to inject Jazz.atk (I haven't tried any of the other attack files yet), it corrupts the level. Injecting masks and animations works fine, it's just attack files. I haven't tried events or special behaviors.

Sure you've got the right version of JJ1? I think you need 1.3