Alright, well I've been looking into this a lot myself. I am particularly interested in enabling the 3D slider on games where it's disabled. Even though it doesn't fully enable 3D, I like the effect of the parallax barrier being activated and the full screen of pixels being used.
If this worked on Dragon Quest 8, it would fix my biggest issue with it—the font. And I know it does, because I tried it, and it looks great. Besides the fact that the right eye's image is all screwed up. And, for the record, there is absolutely no FPS loss doing this. Just the issue of the right eye image.
So, the code that's generally used for situations like this has been something like:
D3000000 00000000
0042A1F4 00000702
D2000000 00000000
This is for Bowser's Inside Story, in particular. The game has absolutely no 3D, but this code will enable the 3D slider, activate the parallax barrier, and in my opinion, make it look nicer.
I have no idea how these codes were found. Playing around with the 3D slider generally brings me to completely different values in the hex editor. However, I looked at what the value is before the code is implemented. It's always 00000700. So I searched for 700 and managed to find the correct value in a bunch of games, including DQ8.
Playing around with the value, I realized that flipping it to 701 instead of 02 brings about a different screen mode in which each eye's image is displayed on each side of the screen, without any 3D. In some games, such as Mighty Gunvolt, I realized that it showed a perfectly mirrored image on each side in this mode. In other games, like Mighty Gunvolt Burst, the second screen is a bit garbled and flickers constantly (sometimes that flickering can persist even after closing it). This is also the case in DQ8 and others.
However, the garbled right eye image does not seem to be an indication that the 702 code will fail or not. Mighty Gunvolt Burst works fine, though it might crash when you exit to the home screen. DQ8 works as well, but the right eye displays a severely darkened image. Other games that display this behavior with the 701 code may just crash with 702, such as Final Fantasy Explorers.
HOWEVER, I noticed something interesting with Bowser's Inside Story. It shows neither a perfectly mirrored image nor a garbled second image. Instead, the right image shows nothing at all. It's entirely disabled. Nonetheless, the 702 code works perfectly. Thus, the right eye image is actually unnecessary for this code to function.
This brings me to somewhat of a dead end, but these are my findings.
If a code could simply disable the right eye image, it is possible that these other games could work with the 702 code in the same way Bowser's Inside Story does. But that is just a guess, based on the fact that I'm assuming these games just have something set weird or set to null or something which causes it to screw up in 3D mode.
DQ8 seemed like a great testing candidate, because the battle records screen switches to 3D. So you can theoretically see what is actively changing. It does change that value to 702 when you go into the battle record. And changing it to 701 on that screen provides a basically slightly offset mirrored image on each side with no graphical issues. This is the intended behavior in games that support 3D. So something else is changing between going into the battle records and leaving it, obviously. However, my limited knowledge didn't get me much further at that point.
