In Scratch 3.0 projects cannot be saved on the website if their JSON file occupies more than 5MB. But wait, this one does! Click see inside and look at the variable called "super long variable". It's length is of over 8 million, so that means the file will be at least 8MB. Try remixing the project, it won't let you save it unless you delete the variable! The way I did it was I created the project in Scratch 1.4 and uploaded it from there.
