Whenever I do more than 1 loop. Just simple loops such as:

when green flag clicked
forever
wait (0) secs
change y by (-1)
end

Even when the only thing in the project is 2 of these loops & nothing else everything lags until one of them stops.
I see almost all other games having a lot of things moving, rotating, clones & so on. But that doesn't lag at all.
Why does it lag for me in my own projects with multiple loops?

As I recently learned there are many more ways to do loops than using a forever loop. And also if you are wanting to use forever loops then make sure they aren't always running! Only run them when they are needed. A simple way of doing that would be with broadcasts. I'd appreciate if you could share your project so I could take a look and see if I can help in any way.

Hoping that helps,
~ Jamie