For specific Windows info,scroll to the bottom! I've added links to all the necessary tools in the requirements. If you have WIndows-specific questions, feel free to ask! And yes, all of this works 100% on Deck, and there is no difference in the process. I have the exact same mod setup on PC and on Deck. I.
https://www.nexusmods.com/eldenring/mods/90
to the game's "Game" folder. Add "toggle_anti_cheat . exe" as a non-Steam game and MAKE SURE to launch it before trying Mod Loader or it might not work! Also, this tool makes you unable to go online at all just to be safe. Note that if you ever want to go online, you WILL need to disable all your mods and revert your regulation .bin to stock.
Also, make sure you've ticked "show hidden files and folders" in your DE's file explorer.
II.
Unrar modengine in the ELDEN RING folder, but not in the GAME folder, it automatically detects the game. Add "launchmod_eldenring.bat"
as a non-Steam game, and put WINEDLLOVERRIDES="dinput8=n,b" %command% as a launch command.
III.
edit: As user adraido mentioned, I forgot to add this: you might need to edit launchmod_eldenring.bat to point it to the base eldenring.exe in your drive if you are on an SDcard or on a different drive to your steam install - ModEngine doesn't always recognize it. For deck, for example, you edit it in a manner like this:
.\modengine2_launcher.exe -t er -c .\config_eldenring.toml --game-path
"/run/media/deck/360c883b-7c0c-4b3f-b1f4-3d66dcdedbe7/steamapps/common/ELDEN
RING/Game/eldenring.exe"
The directory won't match yours, this is just an example. For deck, if installed to the SD card, to get the address, just go to "primary" (your mounted SD card), then find your steam library/steamapps/common/ELDEN RING.This is particular to your setup, on a different distro the path might be, for example,
/media/YOURUSER/YOURDRIVE/steamapps/common/ELDEN RING/Game/eldenring.exe.
It then recognizes it and launches without issue. Thank for reminding me to include this, adraido.
Here is what the modengine folder contains. If you are just gonna use this as a loader to add mods, you don't need to change the default
config. This is where the .bat file you need to add to steam is located, though.
IV.
Here is what most mods for Mod Engine 2 you get look like. They're a bunch of chr/event/map/action etc folders that you just paste in this folder and do nothing else, and they work automatically. Just watch out for mods that are conflicting, since those require a much more involved process of merging with Yabber of specific .tae files.. Don't worry, as chances are, unless you want an overhaul mod that contains all these folders, you won't usually get conflicts if you are using individual mods. If you do, choose the one that is more important to you.
V.
Here is what my main game folder looks like. the mods folder is the folder of Elden Mod Loader. The Mod Loader config file and dinput8.dll are also part of it. When you get Elden Mod Loader, unrar in here, NSIDE the Game directory!
VI.
Here is how my Elden Mod Loader mods directory looks. You might notice one of the actual mods is repeated - THAT IS ON PURPOSE! You MUST repeat the first alphabetical mod and its .dll, but with a different name, and you must put them first in the load order of the elden mod loader config discussed previously, because otherwise the first mod will always fail to load when using both Mod Engine and EML!
Other than that, you just unrar Elden Mod Loader mods here and add them to the mod loader config.ini.
VII.
This is your elden mod loader config.ini! You NEED to add every EML mod you use here, in order, or they will not load! Notice the first repeated mod that I told you is a dud, made to take the "1st mod won't load" error!
Small edit, because of NedVedSed mentioning Seamless throwing an error:
Yes, you can use Seamless alongside all your mods if you want! Just install Seamless as normal (so unrar the Seamless archive in /Game), then take seamelsscoop.dll and the seamlesscoop_settings.ini and move them to the EML "mods" folder! 
VERY IMPORTANT! The newly created ModEngine compatdata directory looks like THIS (this is mine):
You will have to copy your ER save file and your Seamless save file to your new compatdata directory!
THE GAME's save directory looks something like this: (this is mine)
home/USER/.steam/debian-installation(or
steam)/steamapps/compatdata/1245620/pfx/drive_c/users/steamuser/AppData/Roaming/EldenRing/stringofnumbersindicativeofyouruserID/
/home/cave/.steam/debian-installation(or
steam)/steamapps/compatdata/3666052718 (these numbers will probably be different for you, but I'm just showcasing it's a separate folder - sort by newest modified)/pfx/drive_c/users/steamuser/AppData/Roaming/EldenRing/
Make sure to start the game via modengine up to where you accept the terms.
Then quit out, and paste your save file(s) in this directory.Additional: If you're wondering about Cheat Engine or that practice tool you saw in one of the folders, JDSD's ER tool is a speedrunning tool for the game that lets you learn specific boss patterns and combos, turn off gravity for screenshots, freeze AI for cool cinematic stuff... plenty of functions. You can use this alongside all your mods, too - install SteamTinker Launch via Protonup-QT. Go to
the game config, fork custom command and point the exe to this tool's exe. Just make sure to have the most recent version.
For STL, I recommend 11.11 or 11.00, because while old, they also support launching CheatEngine alongside the game, and freecamera mods only work via cheat engine. Worth noting, you have to temporarily disable your Elden Mod Loader mods for CheatEngine to properly launch alongside the game, but since you're not gonna be needing it for too long, it should be fine.
As for Merging mods into your regulation.bin via DSMS:
download it, unzip it anywhere in a folder. Add it to Lutris, make sure it can run. Create an empty folder for its wineprefix. Run it once. After that, run wine config, tick "show dot files". When it runs, go to the top left for new project > point to your game .exe (should be able to get to it via /media if it's not in your OS drive. If it is, go to Z:\home\user.steam\steam\steamapps\common\ELDEN RING\Game to point to your .exe, and create a new folder for the project itself wherever you want. Once you press "ok", a whole lot of nothing visible happens, and a project.json file is created in the directory you specified for project directory.. You want to go to Param Editor in the top left. This is where you will be importing most of the mods that are just CSV tweaks. It is as easy as going to the correct row > pressing Edit on the top left> selecting Import CSV > From File > All fields> andpointing to the file you want to merge into your regulation.bin, then saving and overwriting the one in your game folder with the newly
generated one. If you dabble in there a lot, you will learn enough to where you can do stuff like tweak amulet effects, spell slot costs, change the additional effects of weapons, change movesets, etc.
Nexus has some good links on this, such as
https://www.nexusmods.com/eldenring/mods/199/
and this
https://www.nexusmods.com/eldenring/mods/247/
Second link is just as usable with DSMS, just ignore the Yabber-specific stuff.
Advanced editing needs just a bit of practice and browsing the param rows, plus some help on what flags do what from Nexus and this little helper sheets:
https://github.com/MaxTheMiracle/Dark-Souls-3-Parts-Files/blob/master/Elden%20Ring for parts files (for replacing armours)
https://docs.google.com/spreadsheets/d/e/2PACX-1vToIy4TTeHhzWUHrR13IUSCb9SWPIdooxHRplMVuaMjmAvMPK2hXIHYA4JS956yuE7bPgGNx-GNRe1f/pubhtml# for pretty much anything else - Ash of War IDs, etc.
I've tried to make this as simple as possible, and hopefully it will be of use to someone. Most of this will work on Windows, and it's even easier there, as you don't need to add as non-steam game, etc, so it should be helpful to WIndows users as well.
HOW THIS PROCESS DIFFERS ON WINDOWS:
You still follow the same basic steps. Get anti cheat toggler, download Mod Engine 2 and Elden Mod Loader, still place the EML files in the game folder and ModEngine in any directory you want (I prefer the "ELDEN RING" directory), you still add mods the same way as described and you still edit the EML loader ini the same way. You just skip the steps of adding anything as a non-steam game - you just run things directly. Same goes for JDSD's practice tool. That's basically the only difference, other than the save directory, which is in AppData/Roaming/EldenRing. Back up that save, launch with the .bat, accept EULA, quit out, paste save over with your own.
DSMS is also used in the exact same way, except you just don't add it to Lutris, obviously.
