The exception log contains details about where in the code the exception occurred, useful to debug an error. It may be found in the game's root folder, along with the executable. Launching the game clears the file; if you have done so after getting the exception, you will need to trigger the error again to regenerate the log. If, even after doing so, the exception log doesn't exist, it's useful to provide this.
Default Steam path on Windows:
C:\Program Files (x86)\Steam\steamapps\common\Rain World
In Steam, you may open the game's folder with Right Click -> Properties -> Installed Files -> Browse..
To send the file, drag and drop it into the Discord window. Do not copy and paste the contents of the file.
The file provides the function which threw the exception in the code, as well as all of its ancestors down to the main. If the exception is generated by a mod or combination, typically they will be near the top, marked as modifying the recently-called functions. Disabling them may fix the issue.