Introduction

This tutorial will be guiding you from scratch on how to begin modding Super Smash Bros. Ultimate.

Before Getting Started

This tutorial will contain the most up-to-date information on preparing to mod Ultimate.

NOTICE: As you read the guide directly below, please keep in mind that creating an emuMMC is not required and generally not necessary for standard custom firmware usage. It is especially not recommended to use it online as opposed to sysMMC. If you would like to create one anyway, you may do so as you please.

If you are new to Switch hacking, please read up on this guide which will guide you from stock to custom firmware. Be sure to read the FAQ in that guide to answer some questions you may have regarding Switch hacking.

A microSD card formatted to FAT32 is recommended to avoid filesystem corruption. If you have the option to change the allocation unit size, set it to the maximum value of 64 KiB/65536 bytes. Windows by default is unable to format SDXC cards to FAT32, so please use the third-party software guiformat to do so.

To clear up the fear-mongering and misinformation spread throughout the Switch modding community regarding online activity with a modded Switch, please take a look through this GameBanana thread detailing what is safe and what isn't for both custom firmware usage and Super Smash Bros. Ultimate modding.

Having issues with the tutorial? Please consult me in the comments or join the Smash Ultimate Modding Hub Discord server and ask in the help channels there.

DISCLAIMER

I assume no responsibility for any kind of ban or brick by following this tutorial. You take the risk by running the unofficial software. If you follow the instructions exactly as written, you will be fine.

Requirements

• A microSD card of any capacity (a 32 GB microSD card is required if you plan to dump the game for mod creation)
• Skyline
• ARCropolis

Preparing the microSD Card

NOTICE: For any directory in a path that does not exist on your microSD card, create it.

1. Download and extract release.zip from the ARCropolis page.
2. Drag the atmosphere directory from the extracted .zip file to the root of your microSD card. Do this even if you already it on your microSD card, but do not drag it on top of itself!
3. Download and extract skyline.zip from the Skyline page.
4. Drag the exefs directory from the extracted .zip file to sd:/atmosphere/contents/01006A800016E000/
5. Create the path sd:/ultimate/mods/ for you to place mods in.

Adding Mods

The gist of the process is downloading a mod and extracting it to the mods directory. Mods may come packaged in archive formats unreadable to your preferred operating system by default, such as 7Z and RAR. Be sure you have third-party software installed to handle them, such as 7-Zip.

The following layout allows for the storage of mods separated into their own directory. An example path is given below, starting from the root of the microSD card:
sd:/ultimate/mods/Shiny Mewtwo (Default Eye)/
"Shiny Mewtwo (Default Eye)" is the uniquely-named mod directory, and within it is the mod content's root arc directories (effect, fighter, stage, stream;, ui, etc.). You can have as many of these mod directories as you want within the sd:/ultimate/mods/ path and they can be named anything.

Ensure any one mod directory does not have one or more mod subdirectories within it. For example:
sd:/ultimate/mods/25m_release_110/25 m/
This path will hinder ARCropolis from loading any mod content from that particular path.

Skyline Plugins

NOTICE: Only necessary to follow if the mod comes with an .nro plugin designed for Skyline. If the file is named plugin.nro, leave it in the mod directory and skip these steps.

1. Add the plugin .nro file(s) into the following path, starting from the root of the microSD card:
sd:/atmosphere/contents/01006A800016E000/romfs/skyline/plugins/
2. To load these plugins in-game, simply launch the game.

SaltyNX Plugins

NOTICE: Only necessary to follow if the mod comes with an .elf plugin designed for SaltyNX.

1. Download the latest release of SaltyNX here. Extract the .zip file, merge the atmosphere directory with the one on the root of your microSD card, and add the SaltySD directory to the root of your microSD card.
2. Inside of the SaltySD directory, create a new subdirectory named plugins, and inside of that, a new subdirectory named 01006A800016E000. Inside there is where the the plugin .elf file(s) belong.
3. To load these plugins in-game, simply launch the game. Holding L to prevent mods from loading will not prevent SaltyNX from executing these plugins as SaltyNX is not a part of LayeredFS whatsoever.

Updating Compressed Mods

NOTICE: Only necessary to follow if you downloaded a mod that was uploaded roughly around late 2019 and has not been updated since then.

Compressed mod files can be recognized by identifying a hexadecimal value as the file's name (e.g., 0x14C2014A8). These files are compressed with Zstandard and are named after their data offset in the game's data.arc file. If you do not know what that means, don't worry about it. What you do need to know is that these offsets are generally version-specific, meaning they are not supported on different game versions. ARCropolis is unable to read files named by offset and without a valid file path, so they will need to be updated to conform with modern standards.

1. You will need a Python script called OffsetModUpdater. This Python script decompresses every compressed mod file and reorganizes everything into a structure understood by ARCropolis.
2. Download and install the latest Python 3 release if you haven't already.
3. Move the target mod directory to be in the same directory as the Python script. Double-click the OffsetModUpdater.py script. If it asks to install Zstandard, install it.
4. When asked for the mod folder path, drag the directory to be updated into the Command Prompt/terminal window.
5. When asked for the mod version, input the version that the mod's offsets were made for (e.g., 1.0.0). Usually the submission page for the mod says what version the offsets were for, so use that information.
6. The new mod directory will output to wherever you have the script. The subdirectory inside of output will contain the mod directory you can use for mod installation.

Running Mods

To run mods, simply launch Super Smash Bros. Ultimate while in custom firmware. If you are using ARCropolis and this is your first time installing it, you should receive a popup that prompts you to enable newly-added mods. If all went well, you should see ARCropolis's version on the title screen.

As of ARCropolis 3.0.0, you will need to enter the in-game mod manager to manually enable or disable mods. This menu can be accessed either on game launch by holding the start button after the first click of the Joy-Con loading animation or from the eShop on the game's main menu (not the Switch home menu), and then entering the "Mod manager (ARCadia-rs)" option.

If you are having issues with getting mods to load or not crash, please see the first FAQ entry titled "Why are my mods not working?"

Conclusion

By the end of this guide, you should be comfortable with the basic process for modding Super Smash Bros. Ultimate. If you have any questions, please let me know and I'll be sure to answer you as soon as I can! Alternatively, please look through the FAQ to see if something there answers your question.

FAQ

Q: Why are my mods not working?
A: There could be a multitude of reasons for this, especially between which system and what "not working" means. The below will contain some select few solutions per each system.

ARCropolis:

• ARCropolis crashing: Typically when the problem is not related to mods loaded by ARCropolis, it has to do with its configuration or cache that it generates. First, try deleting sd:/ultimate/arcropolis/cache, and if the problem persists, try deleting sd:/ultimate/arcropolis/config
• ARCropolis mods crashing (1): This may be due to the archive bit being set on one or more folders. To keep it brief, when the archive bit is set on a folder, it is read as a file on the Switch's OS. To unset it for Hekate users, click on the "Tools" button, then "Arch bit • RCM • Touch • Pkg1/2." Here, you will find an option titled, "Fix Archive Bit." Select this option to automatically resolve any archive bit issues.
• ARCropolis mods crashing (2): If the archive bit fix did not resolve your problem, ensure that ARCropolis mods are the issue that is actually causing your crash by renaming the mods folder in sd:/ultimate/ to something else, anything else. If this resolved the problem, then you will need to find the problem mod(s). This can be done by starting with a populated mods folder that has all mods disabled from the mod manager, slowly trickling back in enabled groups of mods, testing those mods in-game for a crash, and repeat.

Skyline:

• Skyline plugins crashing: The most likely cause of this is that you are missing dependencies (extra plugins) that a mod expects to work at all. For example, you might be missing libnro_hook.nro, libacmd_hook.nro, or libsmashline_hook.nro, but ultimately it depends on the mod. Please refer to the mod page for a list of dependencies, or contact the mod author if no dependencies are given and their plugin is what's crashing for you.

SaltyNX:

• SaltyNX plugins crashing: This could be the cause of two plugins hooking the same function or if a plugin hooks a function via an offset not for your current game version. It's not exactly feasible to know how or if this is the case for a crash, but it is one worth noting. There's no real way to fix this without contacting the author about it or removing the plugin.

Q: I want to start making my own mods. How can I get started?
A: You will need access to the game's resources to build off of. This question will be split up between three different questions below.

Q: What is the data.arc file, why do I need it, and how do I dump it?
A: The data.arc file is specific to Super Smash Bros. Ultimate for containing all of the game's assets into an efficiently packaged file archive within the ROM filesystem of the cartridge/title. You will need it to gain access to the game's assets for mod creation. If you would prefer not dumping the file and just access it over the network, download ArcExplorer and follow this guide to do so.

Otherwise, if you'd prefer to have a local copy of the file, follow the steps below. For simplicity's sake, you should use Ultimate Mod Manager for nothing more than dumping the game.
1. Put the .nro file from the embedded link above inside of the sd:/switch/ path on the root of your microSD card.
2. Launch Ultimate Mod Manager from the Homebrew Menu by holding R and launching Smash. You should immediately be presented with the application's dumper screen.
3. To perform a verified dump, hold R and press A or Y (depending on the format of your microSD card). Doing this should help ensure that the dump is a "good" file. A list of good MD5 hashes for the data.arc file can be found here.
4. After the dump has completed, shut down your Switch and insert your microSD card into your computer. The dump will be stored in the following path:
sd:/atmosphere/contents/01006A800016E000/romfs/

The result will either be a file or a folder named data.arc. On exFAT formatted microSD cards, it could be either because there is no practical file size limit. With FAT32 formatted microSD cards, there is a 4 GiB file size limit, so any files greater than that size will need to be split and inserted into a folder with a special bit known as the archive bit applied onto the folder for it to be read as a single file on the Switch's OS. If data.arc is a file, simply move it to your computer or preferred disk and read the Q&A after the following one. If it is a folder, follow the Q&A directly below.

Q: How do I combine the data.arc folder into a file?
A: For Windows, run the following command in Command Prompt inside of the dump's romfs folder (see video here on opening Command Prompt in a specific directory) (do not replace %UserProfile%):
copy /b data.arc\* "%UserProfile%\Desktop\data.arc"
This may take some time to complete. Once you are able to type in the console again, it has completed. Confirm the data.arc is one file within your output directory and that it opens in ArcExplorer (as discussed in the next entry). If all is well, delete the data.arc folder on your microSD card.

For either Linux or macOS, open a terminal window with the current working directory being the dump's romfs folder and run the following command:
cat 00 01 02 03 04 > ~/Desktop/data.arc
This may take some time to complete. Once you are able to type in the console again, it has completed. Confirm the data.arc is one file within your output directory and that it opens in ArcExplorer (as discussed in the next entry). If all is well, delete the data.arc folder on your microSD card.

Q: How do I browse the data.arc file?
A: You will need an application named ArcExplorer to do so. Please read the repository's README.md file here to get familiar with installation, usage, and features of the application.

Q: Am I able to add mods without constantly taking out my microSD card?
A: Yes, you can! In fact, this is recommended as constantly ejecting and inserting the microSD card will quickly wear out the console's reader. By using an FTP client, you will be able to send files to your microSD card over the network. I personally recommend the sys-ftpd-light sysmodule to use anywhere, anytime. From there, you can setup an FTP client to access the server and manage your microSD card. Tutorials for setting up a client can be found elsewhere online.

Q: How do I fully migrate from Ultimate Mod Manager to ARCropolis?
A: All listed directories start from the root of the microSD card:
1. Delete sd:/atmosphere/contents/01006A800016E000/romfs/data.arc
2. Delete sd:/UltimateModManager/backups/ and sd:/UltimateModManager/compTable.backup
3. Rename the UltimateModManager directory to ultimate.