Hi, I dunno if awakening this topic is really what I should be doing or if I should have made a new one (since there hasn't been very much discussion in this one about tricks found later than 2008) but anyway this is what I'm doing now.
Anyway, I've been casually speedrunning this game for a little while now and in learning where the game is at at the moment I've noticed that there is one trick that has been found at some point that isn't used in the TAS, which should be able to save a little more time. I haven't been able to find it mentioned on SDA or here so I've investigated it a bit (really hoping I didn't just fail miserably at searching, that would be embarrassing :x ).
It wasn't me who found the trick but I don't know who did, so I'll name it "crawl jumping". Basically you press down, right and jump on the same frame and hold jump for at least 2 more frames when up against a left facing wall. This will cause you to do a crawl animation while jumping, and once the animation ends up until the time that it would actually end if you were on the ground (I believe it was 25 frames) you can do a second jump off the wall.
The window for doing the second jump depends on how long you held the jump button, because the time at which you can do it only starts just after you stop gaining height (you kind of twitch upward a bit, presumably to the nearest tile). Because of this doing small jumps is extremely reliable even in real time, whereas doing bigger ones is up to frame perfect. This is far more reliable in real time than the old way of doing the Shades skip though.
These jumps can be linked together indefinitely by the following input: Do initial crawl jump -> hold down forward and jump 1 frame then jump another 2 frames -> repeat when you reach the jump frame window. This isn't useful however because of two things.
Firstly, as far as I've been able to find out this is only usable on left facing walls, so you can't use it to skip the suction cups or such (though that might not be possible anyway because of the more limited capabilities of the technique in relation to wall climbing).
Secondly, it's not possible to crawl jump off ice (only real ice though, frozen enemies do work) so it's not possible to do something like climbing up the hole from the door leading to the temple (which could potentially have been used in 100% to get the medicine by a better route).
Despite the problems it could save some time in the any% category mainly by doing a jump off the wall with the climbing thing right at the start of the game, rather than waiting for it to come down (in fact, this is a point where you can do the super reliable large frame window jump, so I even use it in my real time attempts) and by doing the Shades skip slightly faster.
It can also be used to get the hammer early in 100% by doing a charge swap to freeze an enemy and doing a crawl jump off it onto the platform.
This trick also works on console (have tested). Also, here is my real time pb (which uses the trick) if anyone's interested (don't mind the slight video editing error at the start):
https://www.youtube.com/watch?v=bJzTpdoexQ4
I haven't tried TASing the game any as of yet, but it's still on the table.