I was a fool not to re-enable my router blocks for the NUS sites and my Wii U 32gb got upgraded. Was about to buy another Wii U when it dawned on me that I still had a backup of my MLC (emmc) and my SLC (nand) on my SD card and on my PC. So as of right now, and few bottles of rum later, I am back on 5.5.1. My guide will be simple because I will just point you to the relevant stuff that's needed to pull this off. Thanks to @Kafluke and @Leeful @EyeKey @dimok789 @koolkdev for their guides and tools. Note: This is not for the faint hearted. You will be doing micro miniature soldering and you need a solder iron with a very tiny tip. Weller Long Conical Tip, 0.4 MM, 800° F http://www.frys.com/product/1486203? Another tip (no pun intended), always use fresh solder. After every use, clean your soldering iron tip and apply new solder. This makes soldering so much faster and you only have to hold the soldering on that spot for less than a second. WHAT YOU'LL NEED Pre Setup You need some type of backup from one of the following: Rednand on SD card or Wii U Nand Dump or Backup of otp.bin, slc.bin, mlc.bin I DON'T HAVE otp.bin! Otp.bin If you have rednand and way back you only got the three files (slccmpt.full.img, mlc.full.img, and slc.full.img) and you never did anything with the SD card you extracted the nand images from, guess what you in luck. Use sdio nand manager to get the otp.bin from the SD card. While you at it, dump all 5 images under nand manager at least three times and then do a HxD comparison of the files to make sure you don't have errors during the extraction. dimok789/sdio nand manager https://github.com/dimok789/sdio_nand_manager/releases HxD - Freeware Hex Editor and Disk Editor https://mh-nexus.de/en/hxd/ Fix you nand using Eyeful tools. SLC nand wrong size. Use EyeKey Wii U NAND Tools https://gbatemp.net/threads/release-wii-u-nand-tools.465386/ nandFixer.exe <input rednand dump> <output dump> adds missing information to your nand nandBinCheck.exe <path to dump> <options> checks that your nand has everything and has no errors. Once you get no errors then you the use the slc.full.img or slc.bin file for the below. Soldering and Restoring *****NOTE: You can't restore just one or the other. If you restore just the nand, you will still see that you are software version 5.5.2. If you restore just the eMMC, you will get brick screen or Error code 160-0103. You must restore both slc.bin (slc.full.img) and mlc.full.img to get back to 5.5.1. I spent a whole week troubleshooting to tell you this. Teensy for the Nand Follow Kafluke's HardMod CBHC Unbrick guide https://gbatemp.net/threads/guide-kaflukes-hardmod-cbhc-unbrick-guide.476725/ You will flash slc.full.img or slc.bin to the nand And this will take 3 hours to flash. SD Card and Reader for you eMMC nand Leeful "Successfully dumped WiiU EMMC nand with hardmod." Guide https://gbatemp.net/threads/successfully-dumped-wiiu-emmc-nand-with-hardmod.457165/ Win32diskimage https://sourceforge.net/projects/win32diskimager/ Depending how good your soldering is, restoring from the sd card reader can take up to 2 hours or as quick as 30 minutes. @Kafluke mentioned that he didn't have to cut the CLK trace. So before you cut the trace, try reading the eMMC image 2 or 3 times and compare using HxD. You may get lucky if your SD card reader has a stronger clock signal. For me I had to cut the clock trace and create a jumper. Tried it without doin it. Didn't work. I can confirm all entry points still work after downgrading and I am spending the $6.99 to buy Brain Age to install Haxchi after finishing this guide. ***Note: Just finished downgrading. I paid my $7 bucks for Brain Age. Couldn't get it to finish. If you click on Download Management, you will see the update to 5.5.2 (it won't say this but you can just assume) with a X, because you most likely have it blocked via DNS. Just click on the update and you will be presented with a option to delete content. (I don't remember actually what it said.) Delete and your ds game will download and install. Tip from @Jhynjhiruu: check eshop to see if you got Brain Training for free. He created a account and it just showed up. Pour me a drink!!!