Hi guys, It's not really a trick about programing, it's just pure animation effects. The collision points are on the shadow. You can make the shadow and the player in different sprites objects and then make the shadow follow the player by the everytick set position to player image point etc... or integrate it in the animation like I did in my example. Well make the player falling to a hole with this method, I think you need to make a "falling animation", if the jump animation finish or you are in the default animation, or in the "walking/running animation" etc...and your shadow it's overlaping the "hole" start the falling animation and disable the 8-direction until the animation finish, well that's just an idea. The thing is that it's not really a code of programing the jump to move up and down. The animation make the ilusion of jumping. See the image bellow.
<center><img src="http://dl.dropbox.com/u/58103549/Jump%20animation%20example.png" border="0" /></center>