Most Mashups draw alternate lines from two pictures. Other Mashups use colour transparency, differently coloured pictures and pixel colouring randomly from either picture. The pictures are drawn with Pen from RGB colour lists. I call the last picture "The Monster Mash". I scanned all the images in this project using a fast scanner made from the griffpatch video tutorial. https://youtu.be/3lz1nylUHiY Scratch has size limits and will not save projects with 2 lists each with 172,800 RGB colour entries! This project uses lower resolution pictures instead. Scratch can save projects with up to 6 lists each with 43,200 RGB colour entries, ie. 240x180 resolution rather than 480x360 resolution above. (Saving 7 lists is unreliable).
