The most major progress I've made this month is that I beat the game on Hard difficulty for a first time without mutators on NG. I obviously did it before release, and not even once, but with developer cheats for testing purposes. And it turned out exactly as I anticipated: it is as much more difficult than Normal as Normal is more difficult than Easy, with minimal damage and health modifiers.
I also finally found a reason to update the game and, for the first time since release, update the demo, but generally for the sake of reminding myself of this process.
I finally managed to design a laser rifle. I tried it and gave up many times, even though I supposed to arm Angel with it, but I didn't, so in the release she was armed with something that is labeled as "Combo" in the game files. Laser rifle might be one of the first weapons when I finally start adding them.
To be exact, this is the most major progress that I was able to interpret. Generally, I am still working on the zone editor. However, I want to prepare something interesting by the end of October.