could someone help me with a mask?

[undeath]

I interpreted this is was that the "-b" was the main "opening" command, with "sub" commands denoted with the double dash.

generally, commands on the same line denote equivalent options -b is the same as specifying --benchmark. This is true for almost all cli applications out there.

A complete example of a custom character set and its use in a mask would be easy to add but is missing.

There is a specific example section for mask files… https://hashcat.net/wiki/doku.php?id=mas...k#example1

An example using a comma for a mask file is never given on the wiki. How would I know I can do that without asking?

[?1],[?2],[?3],[?4],[mask] -> apply common sense when reading