1. Are using mods online safe for Smash Ultimate?
There have been false rumors since 2018 that just running mods even outside of the online mode and locally can ban you due to you having to mod your switch/install a custom firmware (CFW.) These rumors are false. Many threads like this, that, and even over on other sites like this have outdated information or assumptions that are no longer true or were never true in the first place.
Generally, Smash Ultimate mods are on the same level as Smash 4 in terms of being safe to use Online outside of a few cases. If you've pirated your copy, you won't be able to use this FAQ. We advise you purchase a copy of the game to play and won't support pirates in this FAQ or elsewhere in the scene.
Mods that change the visuals 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), music, and UI.
Mods that change the overall experience of a match like moveset mods, parameter edits for fighters and stages, code edits, etc. are not Wi-Fi safe and will immediately disconnect you from a match unless your opponent(s) have the same exact mod setup in terms of mods that could cause disconnects, like in Smash 4. What this means is that you'll have to use the same gameplay mods or else you will both desync from an online arena.
For example, if you had the same gameplay mods installed, you will be safe and not disconnect. 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.
2. How do I not get banned while on custom firmware?
First things first, using Atmosphere alone does not put you at risk for a ban. The console is unable to detect whether you are running it or not by itself. It will not scan your microSD card for custom firmware files either, as that is illegal for Nintendo to do.
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 enough grounds for a ban. Changing your user profile picture to a custom one is also an instant ban.
Modding and cheating in online games is a probable ban. Super Smash Bros. Ultimate does not entirely fit within that category, so read below:
Using mods online for this game is OK, but do not use online if you are loading a code mod(s) that change the 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 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 a code mod.
Do not upload modded replays or videos online to the Shared Content tab. Do not use Giga Bowser or Individual Pokemon or use any normally inaccessible characters online. The same goes for the extra stages mod, which I would not have installed at all if you plan to play online. Do not upload Miis that you created while mods for said Miis costume/hat were loaded into the game.
It's also important to note that most bans reported have been on the user's error and not because their ban was somehow unavoidable. If you follow the steps accurately and to a T, your chances are minimalized. However there is always a risk, so be cautious and careful as to not compromise your online.
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, 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 if the mod's changes are Wi-Fi safe.
- Mods that change Gameplay are only safe in Battle Arenas in 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 and in very, very fringe cases, may get banned. However, this would require Nintendo to comb over your match error specifically out of the many thousands of play reports they get on a daily basis and is something you will not have to worry about if you're still abiding to the rules in the steps above and not pirating any games or getting messy with your system.
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 or have it at their disposable and another for general usage and gaming.
That being said, have fun and if you need to actually figure out how to start modding, there is a guide that gets regularly updated. Have fun and if you need any more help or support there is a modding discord with a faq channel with much more extensive general explanations on things like advanced texture editing and code edits.
Disclaimer: I'm not responsible for any issues or bans caused by any of this FAQ. You are taking the same minimum risk as you would when modding a game like Smash 4 in that you are still modding your console. This is not a recent discovery or specific to the Switch. These steps are also commonly known in the community and generally agreed upon advice. It's also not my fault if Sakurai himself shows up outside your window to make sure you're not using that cool Mario recolor you found.
Also, thanks to ThatNintendoNerd for the base post that this was modeled after.