Backward shell hyperspeed

"Backwards shell hyperspeed" is gaining backwards speed constantly by riding a shell and going backwards via slopes. This can be used again on a nearby slope to continually gain backwards speed. This is used in the A button challenge.

Execution

While riding on a shell, move upwards on a slope. You'll notice mario moving backwards. If you angle mario slightly uphill, almost parallel to the slope, you gain backwards speed. Keep doing this to gain a lot of backwards speed, and possibly clip through walls