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Skyline & ARCropolis Help FAQ

A Forum Thread for Super Smash Bros. Ultimate

What is Skyline? 

Skyline is an environment for developing code mods, similar to SaltyNX. Skyline is not what will lift modding restrictions, as that will be handled by the ARCropolis plugin which was developed in the Skyline environment.

How do I install the ARCropolis plugin? And what does it do? 

This plugin allows for arbitrary file replacement with files of arbitrary size, meaning you can load mod content off of the microSD card with any file size without the need of a data.arc on your microSD card and not having to deal with compression issues anymore, something especially useful for more complex mods that were impossible before it existed. 

This plugin does not properly support NUTEXB and EFF files at the moment, resulting in a crash when loaded, but it is planned to be supported later on. All mods that currently use ARCropolis seperately install these formats via Ultimate Mod Manager for this reason

File redirection has also been partially surpassed, however this is still a bit buggy and doesn't work successfully under certain conditions. You cannot add files with this plugin yet. 

1. Download the ARCropolis plugin from here ( This plugin includes a prebuilt release of Skyline. 

2. From the ZIP file, drag the atmosphere folder to the root of your microSD card and allow it to merge any files it asks, only if prompted. 

3. Inside of the /atmosphere/contents/01006A800016E000/romfs/ directory, create a new folder named arc. Inside that folder is where you're going to place your ARC root folders (fighter, stage, stream, ui, etc.). 
3a. Alternatively you can have an Ultimate Mod Manager style layout for your mods, where you have them split up between folders. You won't need to "install" these, as they'll be automatically loaded into memory if they are present. The directory is as follows, starting from the root of your microSD card: /ultimate/mods//

I installed it but my files/plugins aren't loading? 

Check if you have this file /atmosphere/config/system_settings.ini. If you do, open it and change ease_nro_restriction = u8!0x0 to ease_nro_restriction = u8!0x1. Save the file and boot back into the game and see your results. Reboot your console if done over FTP. If you do not have this file or if you do have it and have done the changes but still experience no change, please refer to the  Smash Ultimate Modding Discord for further assistance.

Why is Skyline crashing for me? 

One reason could be you have both subsdk1 and subsdk9 in your exefs folder. These files are standard libraries. In Smash's case, it has multimedia decoding and such. Skyline is compiled into one of these subsdk files, so if you have two of them, Skyline ends up loading twice, causing a crash. This can simply be solved by removing one of these files (preferably subsdk1). This is not the only reason however, so please refer to the Smash Ultimate Modding Discord for assistance if this did not fix the issue or does not apply to you. More fixes may be documented here in the future.

For macOS users: You may have hidden files beginning with ._ in the file name. These files contain file metadata, and if Skyline finds them it causes it to crash. This can be circumvented by simply removing these files with a terminal command:
dot_clean /Volumes/
Where is the name of your microSD card (replace the angle brackets too!). This will be fixed for Skyline later on.


Credits to TNN for the base post this was modeled off of from the Ultimate Modding Discord's #faq channel.
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