Potion Explosion 2nd edition uses plastic for the marble holder instead of cardboard. The hopper in my copy is crowned at the centre and the marbles roll immediately to the far left and right holes.

This part sits in the hopper and levels it out somewhat so the marbles flow to all 5 holes on a level table.

I printed in PLA w/ 0.15 layer height.

Leave it to cool to room temperature on the plate, or it will develop the same crown.