Variable Width is the 1st Master Extra stage of Super Monkey Ball 2, Super Monkey Ball Deluxe, and Super Monkey Ball Banana Mania, the 291st Ultimate stage without continues in Super Monkey Ball Deluxe, and the 131st Marathon stage of Super Monkey Ball 2 in Super Monkey Ball Banana Mania.
This stage involves a platform leading up to an elongated appearing version of it. There are several incredibly narrow, long platforms that move down in a sort of arc, and which then reform to build a bridge. The goal is at the end. The bridges, however, don't reach all the way to it, making the player having to leap into it.
To get to the goal, go straight down the center, starting at about 59:00 seconds, until you can see the missing arc at the end. Then, fall down to a side, and then aim yourself into the goal when you can hit it without falling in the center or bouncing off the goal post. You need to fall as late as you can, so you will have a smaller chance of falling out.