The combinations are only limited to the number of runs you create and place into position. The trick is to use strong magnets like rare earth magnet (they are not really rare). Stick them to your fri.
An oversized cross between pachinko and a marble run, this interactive installation invites people to place cardboard tubes of various length and diameter onto a grid of pegs protruding horizontally from a wall.
DIY Marble Run Craft, This peg board marble run involves creating a clacking, whacking gumball machine that runs without electricity, all with parts found in the kitchen and toy box. A complete operation tutorial was provided.