[Guide]Easiest and safest way to downgrade from 6.0 to 5.0

Here is what I did to downgrade from 6.0 to 5.0:

1- Download and Install all the required drivers for Asus zenfone 2
https://yadi.sk/d/NQCiY--IsQjBr
2- Download the asus flash tool 1.0.0.23
https://yadi.sk/d/NQCiY--IsQjBr
3- Download the latest raw image WW_ZE551ML_2.20.40.184_20160504.raw
https://yadi.sk/d/4cuw246vryaZA
4- Use the ASUS flash tool to flash the raw image
-Double click the ASUS flash tool Icon to launch it
-reboot your phone on bootloader mode and connect it to your PC
-Choose your device from the list which is in ASUS flash tool
-Locate the raw image
-Click on the serial number which appears on the screen within ASUS flash tool
-Select wipe data
-Click the start button to start flashing
-Wait until you see the message successfully flashed

Note that the whole flashing process takes about 6 minutes.

Enjoy!