I have it where I make a new EVENT > SYSTEM, Time: Every X Milliseconds, 2000 (for example). Then for the ACTION > SYSTEM, Create Object, pick the object, layer 1 (for example), x coor is random(640), and y is 0.
+ System: Every 2000 milliseconds
-> System: Create object HealthPack on layer 1 at (random(640), 0)