I volunteered at a camp that used Scratch this week and they had PicoBoards that I got to play with. Here's a very simple (but fun :) ) project I made.
It draws circles with the radius set as the slider value and the pen size set as the sound. It will clear if it is dark. (Put your finger over the light sensor).
If you don't have a PicoBoard...
You can still use this to see what it does, but it is not nearly as fun. Click the button to set it to the No PicoBoard mode. Use the variables for slider and light. The sound will be detected with the computers microphone.