Download the pre-rooted firmware files from the download links. Enable USB Debugging by tapping on Build Number several times in settings, to unlock the developer options. A pop-up will appear after you connect your phone to the PC, and then you should Enable ‘Always allow from this computer’ checkbox and press OK.
After extracting the zip file on your PC, you should get the system.img file. After this, open a command window in the z2unbrick folder. Now, you should hold Shift key and right click on an empty white space to view a pop-up message. You have to type the ADB reboot bootloader command and get into fastboot/bootloader mode.
Type fastboot devices in your command window and see fastboot is working. After this, you should install the pre-rooted firmware and then flash it using the commands, fastboot flash fastboot droidboot.img, fastboot flash recovery recovery.img, fastboot flash boot boot.img, and fastboot flash system system.img.
After this, you need to factory reset and then run the commands fastboot format userdata and fastboot format cache. After this, you need to reboot your device using the command, fastboot reboot. Your Zenfone 2 should start properly now, without any bricking issues.
Stay tuned for more updates on Asus Zenfone 2!