Here is a video of the marble run alternating diverter in action.
This marble run piece will split marble entering it into two different paths. Multiple of these diverters can be connected to send marbles onto as many different paths as you want!
This should work with almost any marble run set (ours was tested using a Marble Genius set).
The diameters that mate with other pieces are about 23.75mm.
The center lines of both outlets and the inlet are all 100mm apart (your set does not need to match this dimension to make this part usable).
Print one each of the "Main Part" and the "Diverter Paddle". The diverter paddle just slides loosely into the main part with the shortest/thinnest arm pointed toward the marble inlet.
This is a fairly simple print. I recommend 100% infill for the Main Part with very minimal supports (only really needed inside the inlet cylinder).
If you print one, please consider posting a make!