Cardboard box glitch
The cardboard box glitch (not to be confused with Melee's Box glitch) is a glitch that can only be performed in Super Smash Bros. Brawl's Stage Builder.
How to Perform
Performing the glitch
To perform this glitch, the player must create a stage that has a "box" of blocks (or three normal-sized blocks, one to the left, one to the right with a gap of one space between the left block, and a block above the gap, and then a pass-through platform in the gap) with a set of blocks to walk upon underneath it, by just one space.
Then, one must then set the game to a Giant Special Brawl, and play as Snake. Snake must dash to get underneath the blocks so that he will be standing inside the box, with his head poking through the platform. If Snake uses his taunt here, the box will stay once he lifts it up. They can then proceed to do this as many times as the player wants, until the game cannot handle any more on-screen items appearing. Some character's attacks that produce items, like Diddy Kong's Peanut Popgun or R.O.B.'s Gyro, will stop working. Also, when Wario uses his Wario Bike, the bike will appear, but vanish as soon as it falls over.
When Snake drops the cardboard box, it counts as a new item. It's programmed to vanish after a small time, but it cannot vanish if it's in mid-air. Because the giant box is too big to correctly fit into the small space, and because Stage Builder pieces are known to have sub-optimal collision detection (as they're the cause behind other glitches), the box never falls into what it can consider "ground", so it can never disappear.
The following video is a demonstration of the glitch.