I could not find a good marble funnel for our National Geographic/Marble Genius compatible marble run, so I hacked one together.  It works great at prolonging the marble travel time since each marble spends about 7(!) seconds in the funnel, and multiple marbles can be in it at once.  Printing at 45 degrees worked best for me; printing on its side made the layer lines at the funnel outlet prone to splitting when attached to other components, and printing upright caused bumpy artifacts on the outside of the cone that had to be shaved or sanded off.  Give it a try and Boost if you like!