Go to the battle map Double Deck. In the center of the arena there is a raised green platform that you can fall onto from the upper-most deck. Get on it, and slowly drive to a corner of the platform. Align yourself so that you're facing the corner, then slowly inch forward. You'll fall off, and it will seem that you've fallen inside the platform. But you haven't - if you attempt to drive in any direction, you'll pop out onto the lower floor. If another player views you on their screen, you'll appear to be outside, not inside, the corner.
If you get hit by a player with a star while psuedo-inside, you'll pop back onto the top of the platform. If another player does something which causes you to move backwards, like ramming hard into you, you'll actually end up inside the platform, where there's nothing except for water, and you'll respawn and lose a balloon.
Submitted by: Zanto