I know this leaderboard is fairly new, but I'll share this idea anyway cuz its pretty interesting.

Out of Bounds% is where you get your character out of the area/field of view of the DS screen. I don't 100% know how this works, but I somehow managed to do it in this video unintentionally when attempting an Any% run:

The timer starts on file selection and ends the first frame where your character goes off-screen.