I think what's interesting about the "Player shock jump up" line is the fact they deliberately used the unsigned byte representation of -2 (0xFE) when setting Mario's Y speed...

Additionally, you can see the removed lines of code in the official All Stars source code!

From @nfroggy99 on Twitter/X:

"When you look at the All-Stars source code, the equivalent subroutine to BrickShatter (BBKINT) says "Player shock jump up", so you're right that this behavior was intended. I'm glad that they accidentally screwed it up because the All-Stars behavior feels worse."

It should be noted that the temporary invisible solid block is what keeps the gap solid while the block bouncing animation plays, and is also what actually kills the enemies when you hit a block from under them.

It's also possible that they simply just forgot.

This was fixed in Sonic 3 by also applying the modified ground speed cap logic to the air physics.

Another sample.

Another sample.

This, too...

This isn't so noticeable in Sonic CD due to the different nature of its level design compared to the other games, but the beginning of Tidal Tempest Act 1 is probably where it's most noticeable.

From what I can see from the code, it appears that only pulley platforms, vertically oscillating platforms, and Koopa Paratroopas make use of this functionality.

🤫

The reason the cap ended up that way is because the integer portion is set to -max speed, while the fractional portion is set to 0xFF for some reason, which results in that stuttery motion.

Correction: the bit about the platform not being drawn yet while sprites are being processed being the cause is incorrect. It's more likely that it's because sprites at the top of the table in VRAM will just automatically take priority over sprites after it, regardless of setting

If anyone had caught onto the inputs needed to trigger this secret, it's the same input required to activate the hidden Japanese credits in Sonic 1, on REV01!

As well as the code that sets the secret to be active. Note the lack of the intro Skip flag here.

Another bug that prevents this from appearing is that the code fails to set the global variable to skip the intro to false.

Due to this, it never reaches the code to fully set up the hidden credits.

Below is a reverse-engineered estimate of the code where the game sets up the hidden credits.