[ZenFone 2 Q&A, Help & Troubleshooting] yusoffb01:
Backstory

2 years ago, I installed nougat into my marshmallow zenphone. A few days later there was a problem with 3g and wifi, so after some searching, I found out I needed to flash modem.zip, after doing so, the phone no longer boot, bootloader is good, recovery is gone and fastboot is gone. Spent about 20+ hours trying to recover... but to no success. The main problem was using the XFSTK method, it did boot to fastboot, but the damn phone product code becomes a Z00A, so flashing a z008 rom led to fastboot refusing to flash. Flashing a z00a rom led to bootloop...

Since I wasted too much damn time trying to recover, and I needed a phone quickly, I bought a 32GB mi max for $120 and never looked back.... until today 03 March 2018.

Recovering the hardbricked Asus phone easily

1) Install the intel usb soc http://drive.google.com/file/d/0B2oMRhweQ4CHbURUNk1ZTHI2Mjg/view?usp=sharing

2) Disable driver verification in Windows 8/10 by rebooting into advanced menu

3) Install intel usb soc above

4) Download and install Download xFSTK Downloader v1.7 https://drive.google.com/file/d/0B2oMRhweQ4CHbDNQdy1jVUJFcEE/view

5) Download the files for xFSTK and unzip

ZE550ML http://drive.google.com/file/d/0B2oMRhweQ4CHcHg4WXJQckFGOTA/view? Usp = sharing

ZE551ML http://drive.google.com/file/d/0B2oMRhweQ4CHR21YaDdXdUNlOGs/view? Usp = sharing

6) Open xFSTK,

go settings, tick enable GP flag override and use the number 0x800000807

link the dnx fwr, ifwi and droidboot from step 5 as follows: https://i.imgur.com/mKZoUdi.png

7) Make sure your phone is off, click begin download then plug in phone, it will start flashing

Sometimes it fails while flashing firmware, sometimes it fails while flashing OS. Doesn't matter keep retrying. Pressing volume button while plugging in phone MAY help.

8) Once successful, you will see 4 color background, then usb cable image, then fastboot mode. If you fail halfway in flashing you will stop at either one of the images. Keep retrying until you reach fastboot.

9) At fastboot, you are safe. Go charge your phone for 1 hour. If your screen dies, do not press power button, press volume button it will remain in fastboot mode.

10) While your phone is charging, install asus flash tool https://drive.google.com/open?id=0B4uMV7GwfDAEYm5RWTFydXZWOTQ

Download the raw file https://drive.google.com/drive/folders/13In6163G8S9BbjiNlEOF-fOXhVIC0z9r?usp=sharing

11) With phone charged, plug in your phone and open the flash tool. Your phone should appear. If not replug usb cable/change usb cable/port, restart the flash tool and leave it plugged in and wait UNTIL the flash tool recognizes it. It will recognize... eventually.

12) select correct model, tick erase data, and locate the firmware. Once recognized, highlight it and click START

13) After 20 minutes, it will be stuck because of the change in serial number. plug out usb cable, restart program, plug back in.

14) Wait for the program to recognize the NEW serial number, then reflash the phone, this time IT WILL BE SUCCESSFUL and will boot into Android marshmallow.

Miscellaneous steps after unbricking

Unlock bootloader, flash recovery, flash custom firmware, root, gapps