Ghost Effect

I want to make an object disappear on a click by 15 every 0.7 seconds.....reach a point and then reverse so that it reappears every 0.7 seconds. I have used the repeat until, but I am missing something to have it work....
Right now I have the following...
Repeat until (ghost effect)
wait 0.7 seconds
change ghost effect by 15
go to x pick random 190 to -190 y pick random 130 to -130


The (ghost effect) reporter reports a number, basically what percent the sprite is ghosted, 0=solid, 100=invisible.

The REPEAT UNTIL block needs a predicate, i.e., an expression that reports True or False, not a number. Maybe you mean
repeat until ((ghost effect) > 100)