Downgrading LG G Pro 2 from Lollipop to KitKat

The wife recently took possession of a Xiaomi Redmi Note 4X, so her old LG G Pro 2 is mine to play around with. First order of the day is to root it. Lots of tutorials and scripts and tools around. Tried a couple of them, but didn't work. Maybe because the device has already been upgraded to stock Lollipop.

Getting impatient, I decided to use KingRoot. Big mistake. After installing and running KingRoot, it informed me that rooting was unsuccessful. Uninstalled the apk, yet KingRoot still persists. I bit the bullet, and did a factory reset. Guess what? Still there. Once in a while, I'll get a notification from Android asking if I want to disable KingRoot. I tap Yes, but it always comes back. Time for a system wipe.

The idea is to root the device, install a custom recovery, then flash a custom ROM. From what I've read in the XDA Developers forum, this is best done when the device is still on stock KitKat, which requires me to do a downgrade. Now, the problem with an "old" phone is that there are so many posts talking about the same thing, yet many of them have conflicting information. It's up to you to figure out which parts fit your situation. Worse, most of the download links to the ROMs or scripts are now broken. Either the personal domain is non-existent anymore, or the files have been taken down by the file-hosting company.

At the end of the day, I managed to get it done, and this is how I did it.

Downgrade from Stock Lollipop (D83820x) to Stock KitKat (D83810x)
Two ways to do this. Easiest way is to download a KDZ file and flash using LG Flash Tool. Here is the official procedure:
http://www.lg-phones.org/how-to-flash-unbrick-lg-g-pro-2-with-a-kdz-firmware.html

If that looks too complicated for your liking, you can try this modified flash tool from XDA:
https://forum.xda-developers.com/showthread.php?t=2797190

1. copy KDZ file to the same folder as the flash tool
2. power off phone
3. hold down VolUp button, then connect phone to PC using USB cable (a.k.a. download mode)
4. run LGFlashTool2014.exe file
5. select KDZ file
6. click on CSE Flash button

Normal Flash is for when you want to flash ROM without losing any data. Make sure you flash the same exact ROM as you have now, or you'll get bootloops. Used when you need to fix some system error. CSE Flash is for when you need a clean format. Obviously, all data will be wiped. Used when you need to downgrade or upgrade to stock ROM.

Next question is, where do you get the KDZ file? Lots of links on the forum, mostly dead. Well, I've got the link for you. If you're after your current ROM, use this:
http://csmg.lgmobile.com:9002/csmg/b2c/client/auth_model_check2.jsp?esn=<yourimei>
Replacing <yourimei> with your IMEI (15 digits).

You'll then be presented with the download link between the <sw_url> tags. You might also take note of the <buyer> tags, which tells you which region your phone is from.

<response req_cmd="auth_model_check" status="OK">
<auth_model_check>
<result>OK</result>
<esn>xxxxxxxxxxxxxxx</esn>
<model>LGD838</model>
<suffix>ACWTOP</suffix>
<msn>xxxxxxxxxxxxx</msn>
<esn_date/>
<sw_version>D83820B_00</sw_version>
<sw_url>
http://pkg02.cdn.gdms.lge.com/dn/downloader.dev?fileKey=xxxxxxxxxxxxxxxxxxxxxxx/D83820B_00.kdz
</sw_url>
<sw_locale_url/>
<sw_recommand_uri/>
<app_version/>
<app_url/>
<cs_em_flag>N</cs_em_flag>
<cs_em_uri>N</cs_em_uri>
<chip_type>EG</chip_type>
<prod_type>2</prod_type>
<buyer>CWT</buyer>
<file_name>D83820B_00.kdz</file_name>
</auth_model_check>
</response>

Need an older/newer KDZ from a different region/country? This link's for you:
https://lg-roms.com/LG-Firmware-List/LG%20G%20Pro%202
As of this writing, the download links still work.

The first time I ran the tool, the screens are showing gibberish. Window text is possibly in a foreign language, as I can only see question marks. Clicked a few default buttons, and the software quit. Re-ran the tool, and this time the text was in English. First try didn't work because one of the screens has one button to exit from the tool (while in the middle of flashing), which I clicked. Second try worked just fine.

If, for some reason this method didn't work, then you'll have to use flash method #2 mentioned here:
http://www.lg-phones.org/how-to-flash-lg-g-pro-2-with-a-tot-firmware.html
Similar information here:
https://forum.xda-developers.com/showthread.php?t=2475045

From there you can get download links to the flash tool, the crack, and the TOT/DLL files. That said, I wasn't able to find any working download links to the TOT/DLL files that I needed. Good thing the KDZ method worked for me.