Use this to make your own project, remix this one. To make the backdrop change, make it where you wait a few seconds and then switch to backdrop whatever. Watch my other project, it is a good example: https://scratch.mit.edu/projects/1202946415
Just went to myinstants for the sound. I recommend myinstants to anyone who needs audio for their projects. Then again, you could just use y2mate.com LOL Note: myinstants has some inappropriate sounds, so be careful when you go there. Another note: to use a sound from my instants, press onto the sound button, and then download it as a mp3. I promise you that you will not get hacked, I have downloaded many sound effects from myinstants. In fact, I've used it for almost all my projects.