This is, perhaps, the fastest of all 2D games you've seen which really gives meaning to "Sonic". From the top of the screen to the bottom in just 1/30 of a second or 128 pixels per frame max. That's how fast you can get and this is one of only 3 Sonic levels where this is possible (this one in Sonic 2 and two others in Sonic 3).
There are 5 parts to this video. The first 3 parts is where I play as Sonic with Tails. The last two are as Knuckles. In the first and fourth parts, I show you how you get it set up, which requires debug. The second and fifth parts are where I perform the stunt itself. The third part is a slow-motion version of it, played at half speed.
After reaching 128 pixels per frame falling, Sonic suddenly goes up at 128 pixels per frame. This is due to variable overflow. Either an 8-bit or 16-bit variable is used for fractional parts given what I see when doing this. If it weren't for variable overflow, you'd have seemingly unlimited speed. It takes just short of 10 seconds to get to 128 pixels per frame. The screen only scrolls at 16 pixels per frame which is far too slow to keep up with this.