I'm thinking of uploading a pretty old piece of r34 fan-art I made back in July that feature characters from one of my favorite artists (who also allowed me to make r34 fan-art of his characters) but I'm not sure about the tagging rules regarding fan-art of someone else's characters. Should I tag both the artist behind the art (me) and the owner of the featured character(s) as well?

Also, is it allowed to create tags for original species and character names of someone's original webcomic series or should I only use tags that already exist (tagging unknown_species instead of tidri, which is an original species).