Give the falling object the BULLET BEHAVIOUR. Then this will allow you to check the speed of it when it hits the player (or any other object). If it's > a certain speed (the object is falling), then kill the player, otherwise don't (the object is still).
Nimtrix is right, just set the object with the PLATFORM BEHAVIOUR, set the default controls to NO so you can't move it around and check for a collision and if the object IS FALLING. if both are TRUE, kill the player. The way I described it will do the job but is just more work than you need to do.CAPX DEMOvandinz2012-11-12 14:40:52