So, I've been doing a lot of poking around with RAM lately and realized that enemy sub-pixel values (458-45F=x, 478-47F=y) sometimes get inherited from previously killed enemies, and this explains a lot of the headache-inducing randomness that can get in the way of tight optimization. I haven't found any useful applications for this yet though, other that the few I stumbled onto long ago, mostly by dumb luck (like killing one of the boxers at the end of 1-1 on the wrong frame will make Ryu take an extra frame to reach the boss (also, all of the other bosses seem to write their own values when they spawn, oh well!)), but there is a good chance applying this info can still fix some things in stage 6.
Moving on, I'd had the idea that memory relating to the background objects could be read and display something like this:
...and hopefully those elements without a graphical counterpart (and taken advantage of in the published run) would become visible, and maybe other unexpected oddities would appear too.
It turns out this stuff is stored in block 3, in columns of six and starting in the upper left, so it could be interpreted like this:
|300|306|30C|
|301|307|30D|
|302|308|30E|
|303|309|30F|
|304|30A|310|
|305|30B|Well, you get the picture.
So the hex values for the above picture would then be:
|88|00|00|00|00|00|00|00|00|00|D9|00|11|00|00|88|
|11|00|00|00|00|00|70|70|00|00|00|00|00|00|00|22|
|11|00|00|63|00|00|00|00|00|00|00|00|00|00|00|22|
|11|00|00|33|00|00|00|00|00|00|89|70|41|00|00|22|
|88|07|07|07|07|07|07|07|07|00|99|00|11|00|07|88|
|88|07|00|00|00|00|00|00|00|00|9E|00|11|00|07|88|
07=floor
70=standard platform
11=left wall
22=right wall
99=ladder
89=ladder/platform corner
41=grabbable wall/platform corner
9E=ladder to prev. area
D9=ladder to next area
FF=to next stage
63=narrow platform, connected to walls on each side
33=opposing walls (this and the above are the same as the signs in stage 1)
80=platform with corners below it
88=non-grabbable wall (with a weird little platform inside if you can get above it)
83=that weird-ass platform in 2-1b
There are many more, of course, but that covers the most common ones.
Anyway, what I had, perhaps naively, hoped to find was something directly corresponding to what is on screen at any given time, but this doesn't seem to be the case when the game is scrolling. Anyway, none of this really matters much since I couldn't see any evidence of my mystery platforms in memory, or at least why they seem to be in some places and not others. Actually, they're probably everywhere they could be expected, you just can't get inside every wall where they might be.