Just for some clarity get the players Z position, and then add to it however much you want the player to fall.
Player = Game.GetPlayer()Player.SetPosition(Player.GetPositionX(), Player.GetPositionY(), Player.GetPositionZ() + 300)
If you use MoveTo you have to pass in an objectreference and the x,y,z coordinates are offsets from that position.
Player.MoveTo(Player,0,0,somezoffsetvalue,true)
-MM