if you are making a game such as pocket tanks or what ever you can do this to remove the ground: fist you make your ground and then you make a empty movie clip with AC2 then you use that empty movie clip and attach it to your ground and then you draw over your ground and what you do is instead of hitting the ground normaly in most jumping platforms, you do this : if(!_root.ground.hitTest(_x,_y+?,true){
grav = 0;
_y -= gravity;
}
this makes that when he is not hitting the ground he falls letting you fall deeper into the ground, if for example there is a crater and you want to be able to fall in it.
