I analyzed Audiosurf 2's code to find information on all possible skin/mod settings and have written my findings here. I will probably try to keep it up to date as new releases appear.
This documentation is meant primarily to be a complete reference of all the things scripts can and cannot do. While it does make some efforts to be helpful for beginners, it does not yet contain an actual tutorial. The original text in the pages listed below is released under the WTFPL and/or dedicated to the public domain. This documentation is not guaranteed to be correct and may change or disappear at any time.
Some of the documentation content is generated with Javascript so be sure not to block it.
This page was recently mentioned in the the 2022-03-02 update news post. Documentation on the new features is in progress but is not completed yet. If you are eager to experiment with the new features immediately, I am following the #modding-support channel of the audiosurf2.info Discord. As always, I can be contacted directly as well. (see below)
In the meantime, the summary of the new features is that it gives Lua scripts a lot of the Unity engine's power directly, and allows objects built in the Unity 2017.4 editor (including shaders and probably animations) to be used in skins and mods. The full potential of this update is not yet known.
I have posted preliminary asset bundle documentation here.
The official Audiosurf forums are at www.audio-surf.com/forum. Dylan (the game's developer) is known to read and reply to some posts there. There's also the Steam community hub forums but I don't know much about them.
I am also open to helping people directly.
https://github.com/DeathByNukes/as2-doc
This website is hosted on GitHub. If you are interested in making changes or contributions, feel free to contact me or send a pull request.