5 things to note:
- The recommended builds are safesysupdater, julian's sysupdater, and tux's sysupdater. Do not confuse them with the official sysupdater by profi200: The official one was not designed for downgrading firmwares past 9.2.
- Update packs for N3DS/O3DS and console region are completely different. In terms of downgrading from 9.3+, 2DS is considered O3DS.
- If you own a JP N3DS, you must make sure you remove a particular CIA file from the pack before downgrading
- If you own a Mac, you should dot_clean the /updates/ folder with terminal, because the computer likes to add extra hidden files that screw with sysupdater's file-searching abilities
- Downgrading may require you to reset a lot before it finally works: The stars have to align properly for the kernel exploit to allow you to downgrade. When you see non-garbled red text and pressing "Y" says "Getting CIA information...", you've hit the point of no return and should not power off until it's completely done. Take out the SD card after you power off, and when you power on, wait at least a minute and a half with the black screen before declaring the downgrade a failure.