Dynamic shrinking / growing?

I have an image sprite that I need to shrink when flung, and keep shrinking until it reaches y = 20. I can change its size using the set height and width commands, but I want it to keep shrinking until it reaches the y = 20 co-ordinate. Any ideas how to do that? Thanks for reading!

--

Use a clock, every time the Timer event is triggered, reduce the width and height  a little more. Test if it reached the desired size, then when it does, stop the clock.

--