Something interesting I've found in MBG is that you can create a floor that bounces the marble without changing anything in init.cs, which holds all the friction forces and their properties. By changing this to add a bouncy floor is pretty much modding the game, and no one wants a modded MBG, unless its a full on mod, separate from MBG. But, in the init.cs, there is the friction forces for bumbers, which have a force of 15. These forces apply to p-ball_top or whatever its named, but there is also bumper-rubber which isnt used. So if you make a texture named bumper-rubber.jpg or something else that has a bounce in init.cs, it will make the marble bounce. I believe it has the same force as MBP bounce friction (force: 15). There is pretty much useless as we have MBP, but if you want to create an MBG level with bounce floors, you can.