I haven't played the megaman game so I am guessing what effect you are trying to achieve. I suspect you want to modify the platform behaviour so that your gravity value is different depending on the height of the MM sprite - is this correct?
If not, then I've misunderstood and you are probably best just giving the MM sprite a gravity value and letting the platform plugin do its work for you.
If you do want to vary the gravity according to sprite height above the solid then you need to do something like this:
mm Set Platform Vector Y to: 50 + TiledBackground.Y - mm.Y
C2 platform behaviour doesn't seem to like small and changing values of gravity (hence the 50 minimum value in the above example). I tried to insert an image of the event and failed!
Hope this helps....