Read this entire text! It will answer all of your questions. This how to detect whether a project is running in a compiler like TurboWarp or forkphorus. We intend for this to be used to automatically enable laggy features in compilers without affecting normal Scratch or to suggest users to visit a link for a better experience, but ALWAYS allow users to run the project in normal Scratch anyways, even if it's really slow. Not everyone can access TurboWarp. Original Project on TurboWarp and forkphorus https://turbowarp.org/414716080 https://forkphorus.github.io/#414716080 This Project in TurboWarp and forkphorus https://turbowarp.org/958797621 https://forkphorus.github.io/#958797621 How it works: This is not a hacked block or a hidden block. This is an custom block argument reporter. You can create one with "add input (boolean)" while editing a custom block. Normally these always report 0 when you use them outside of a custom block, but some code in TurboWarp and forkphorus looks for this block and makes it report true instead. Other Scratch compilers are welcome to implement this. Thanks to @Executec for the idea of using boolean arguments.