Press the see inside button to see how it works and to start seeing it bob up and down click the green flag. I called a sprite water but you probably want to use colour sensing for this one
there is also jump button code and left and right but i'm saying now the left/right keys don't work the best in water and this is a really hard feature only for the best of the best scratchers my youtube: https://www.youtube.com/channel/UC7vKYOcVSHwzMFW_gK37VuQ
