You should download the custom mod installer. It was made by member Drake and can be found on the download page for levels. The mod changes a file in MarbleBlastGold, so the bouncing on certain textures vary in his level. It's pretty cool if you can get it to work.
You can use Drake's installer. But, I'm thinking maybe it doesn't work with the new, I repeat NEW, MarbleBlast update for Mac. I think it requires Java to operate. I don't know if it a clickable application or if you have to run it from command prompt.
Solo Hans
solo.