1. Will you get banned for modding Smash Ultimate and your Switch for Smash Ultimate?Short answer: No, you won't, but only if you follow the steps correctly and use legal, legitimate methods. In that case, you will be fine, so be sure to pay full attention to this guide. If you've pirated your copy, you won't be able to follow these steps.
We advise you purchase a copy of the game to play as we can't and won't support pirates in this FAQ or elsewhere in the scene.
1.1. Are using mods online safe for Smash Ultimate?There has been lots of false information spread since 2018 that just running mods even outside of the online would instantly or at least likely ban you due to you having to install a custom firmware (CFW) and homebrew on your switch. These rumors are heavily false and vague. Many threads like these and even over on other sites are outdated or at least inaccurate.
Just using Atmosphere, the most popular custom firmware, does not put you at risk for a ban just by using it. The console does not try to detect whether or not you are running custom firmware. Nintendo doesn't bother to detect for custom firmware on modded Switches: they make active efforts to detect cheating in certain games as well as piracy, by checking if an installed game was authentically purchased.
Nintendo does not punish for client sided game mods or CFW by itself, and while they could in the future if they really wanted to, I personally believe this would be very unlikely as the Switch is already well into its life cycle, and they never bothered to issue bans for mods on consoles like the Wii U.
Atmosphere redirects crashes and error telemetry to your SD card rather than sending the information to Nintendo. It will not scan your microSD card for custom firmware files either, as that is illegal for Nintendo to do.
Mods that change aesthetics and audio of the game are perfectly fine just like in 4. This counts as texture edits, model imports (for characters, ones that do not edit the skeleton file's proportions, which is a model.nusktb file change), custom music, and UI.
Mods that change the overall gameplay of a match like moveset mods, parameter edits related to gameplay, code edits, etc. are not Wi-Fi safe and will immediately disconnect you from a match unless your opponent(s) have the exact same gameplay mods setup on their system as well. You'll have to use the same code and/or parameter edits or else you will both desync from an online arena.
If you're still not sure if the mods you want to play with are Wi-Fi safe, ask the creators of the mods you're questioning in the comments or by PM.
1.2. How do I not get banned while on custom firmware?Do not install NSPs under any circumstances while on CFW. This is an instant ban. You will never have to install an NSP to use Smash Mods in any scenario unless you have a pirated version of the game, which is already setting you up for a ban. Changing your switch user profile picture to a custom one is also an instant ban.
Make sure you're using a reliable and up to date guide like TNN's Guide to Getting Started Modding Ultimate. An emuMMC is not required to be safe using mods, but you can still use emuMMC if you wish to. It is redundant for just Smash modding and basic Homebrew, and shouldn't be used online depending on what you do with it. Unless you are extremely paranoid of a ban, setting up an emuMMC is not needed for any type of Smash mod.
Modding gameplay and cheating in online games is a probable ban. Super Smash Bros. Ultimate does not entirely fit within that category outside of a couple instances, like with certain gameplay mods online.
The reason for this is that you should not go online if you are loading a gameplay code mod that changes the game's version string, as it has been found that the version string gets sent to Nintendo at some point after an online match.
While nobody has been banned specifically for this, we recommend you stay safe and temporarily remove the mod that has this issue until the author or another modder removes it. If you are unsure if the version string is edited or outdated, ask the mod author or leave a comment on the mod.
If a mod says that it was based on "code-mod-example", this can also be a warning sign since code-mod-example leaves in an edit to the version string. Just make sure to ask first if you plan to play online with gameplay mods with friends.
Do not upload videos with mods visibly present online to the Shared Content tab, even if you think you could probably go unnoticed. Screenshots will automatically go to shared content when uploaded to Twitter if you do not uncheck the box as well. Do not use Giga Bowser or use any normally unusable characters like him online. The same goes for the extra stages mod. Do not upload Miis that you created while mods for said Miis costume/hat were loaded into the game, as their character portrait will have the modded models and will sync up with the other player online.
It's also important to note that the vast majority of bans reported have been on the user's error and not because their ban was inevitable. If you follow the steps carefully, your chances are minimal and practically non-existent. However, there is always a chance of you the human making an error, so be cautious and mindful of how you use your mods.
Additional note: The training mode modpack that adds things like hitbox display in the training mode can be used online since it only applies to the singleplayer training mode and not any online modes. However, it is prone to crashing the game, so I would take it off temporarily just to avoid that separate (but not risky) annoyance.
1.3. Where can I use mods Online and which ones can I use?
- Anything that doesn't change the Gameplay of a match (character costumes, music, voice packs, is fair game for
Quickplay/Background Matchmaking, Spectate, Online Tournies, and Battle Arenas.If a costume contains a .nusktb file, either the mod author left it in accidentally, or it was edited. If it was edited, ask the mod author or the modding discord if the mod's changes are Wi-Fi safe.
- Mods that change Gameplay (parameter edits of Characters or Game mechanics in any shape or form) are only safe in
Battle Arenasin which both you and anyone who spectates or plays in the arena have the same exact Gameplay mods and the same versions of said Gameplay mods. Otherwise you will desync from the game and the match will stop, which has not been verifiably proven to cause bans, but is still something you should try to avoid out of caution.
- Getting a ban from a Desync would require Nintendo to comb over your match error out of the many thousands of reports they get on a daily basis, and is something you will realistically not have to worry about at all if you're still abiding to the rules in the steps above and not doing anything seriously dangerous. It's still a good practice to avoid them, however.
1.4. I got banned, is there any way I can get unbanned?No method at this time has been found to unban oneself. Some modders have two Switches, one for modding in case they get banned from more dangerous activities outside of smash mods and another for general usage and gaming.
2. Getting started moddingFor a disclaimer, the modding scene is not responsible for any issues that come from following this guide. You are taking the same risk as you would when modding any Nintendo game in that you are still modding your console and breaking Nintendo's guidelines. This is not a recent discovery or specific to the Switch.
The info in this guide is common advice in the Ultimate modding community and generally agreed upon from developers in the scene. Just be careful and ask questions if you need to. It's also not my fault if somehow Sakurai himself shows up outside your window and annihilates you for using Big Chungus.
That being said, good luck, and if you need any more help or support, there is a Smash Ultimate Modding Group that has lots of resources and help channels for assistance. Have fun! If you want to get started with a guide rather than direct assistance, I would use TNN's guide as mentioned and linked above.
Also, thanks to ThatNintendoNerd for the base post that this was modeled after and for helping educate the scene on this topic.