Some people  have had some issues downgrading from 9.3.5 to 8.4.1. This full tutorial should solve these issues. You won't need to downgrade to 6.1.3 first and you won't need SHSH blobs as this method works over-the-air! It works great on my 4[S] and should also for any other 32-bit iOS 9.3.5 devices
  1. Jailbreak 9.3.5 with PhœnixPwn
  2. Let Cydia update, then add the source http://pwn20wnd.github.io/repo/eraser
  3. From there, Search for "Remover" and install it
  4. You'll also want to install a file manager such as Filza
  5. At this point, you may or may not need to respring
  6. Now go into Filza and navigate to /System/Library/CoreServices/
  7. Scroll down till you find SystemVersion.plist and open it
  8. You'll want to tap on the "Root" dropdown and change the ProductVersion to 6.0
  9. Next go to IPSW.me and find the BuildID for your exact device
  10. Now tap on the ProductBuildVersion option and change it accordingly
  11. Once you are 100% sure everything has saved, exit Filza
  12. Open Remover and select the Phœnix Jailbreak option
  13. Let it un-jailbreak your iDevice (shouldn't take more than a minute or so)
  14. Now it should automatically take you into your Settings app
  15. From there, go to General > Reset > Erase all Content and Settings
  16. At this point, you may or may not need to enter passcode/iCloud info
  17. Let your device reset and continue through setup
  18. Once you're in, go to Settings > General > Software Update, and the 8.4.1 update should pop up.
  19. Let the update download and install on your device :D
  20. Once it has booted up, you should be able to setup 8.4.1 like normal! 
  21. Continue thru the setup and if you get any errors, just dismiss them and continue on into the Settings app
  22. Go to General > Reset > Erase all Content and Settings
  23. Let your device reset again, then you should be able to setup without any issues
  24. If you want to jailbreak 8.4.1, you can try the new EtasonJB but beware that some people are having issues with disappearing icons on the springboard. If this happens, the only way to fix it is to restore back to 9.3.5 and then repeat this entire process over again (yikes!) So it seems to prevent this "UIcache" issue, just refrain from installing any tweaks that add an icon on your homescreen.