Forum test. You must click the green flag. Click anywhere to go to the previous costume (costume 3 to costume 1). The first costume you will see is black, second is red, and third is purple. If you look inside the project, the first costume is actually the purple one. I used code provided from @randomguy3513 make a previous costume block. Each time you click, the sprite goes to its previous costume until it reached the first costume (purple) https://scratch.mit.edu/discuss/topic/615463/