So I'm creating this Mega Man project, but after 4 screens of a level, the buster stops working. Is this a cloning issue, or is this another thing I don't know about?

The only stage that works for now is Metal Man's stage, which is on the bottom left.

Here is the project.

Almost certainly hitting the clone limit. The clones in gimmicks are never deleted and if you broadcast spawn gimmicks more than once every clone of gimmicks is creating multiple new clones.

Scratch has a clone limit of 300 clones. do you think you might be hitting that limit?

It's your gimmicks sprite. You're creating the clones via a broadcast (so main sprite and clones are all responding to the broadcast). On top of that, you're not deleting the clones when you leave a screen.

Thanks very much, I didn't know there was a clone limit. I have now fixed the issue and I can continue with my project !