Sadly, these do not seem to be suitable for a scratch card because
a) you get staccato dots, instead of the required smooth swiping reveal, if you do it quickly. I tried changing the project to use Is Touching instead of every tick - same problem. I guess this is a limitation of how often C2 samples the mouse.
b) its not possible to know how much of the canvas was scratched, to complete the reveal and award the prize.
c) it doesnt work on mobile (ipad at least), even if you use touch events. No idea why.