So there are basically two reasons why characters would be considered illegal by Obsidian:
- links invalidation:
[]#^| - file systems limitation:
\/:and?for Android
Other than these most characters are legal, like those emojis being unicode characters, and most other unicode characters, like stuff with accents/diacritics: áāãőůçĉ, and national characters like æøåßþƴðđ.
So feel free to use characters rather freely. See also Internal links and special characters - #2 by holroy