The character "Damascus Steel" is listed as having "Superior Invulnerability (x2)"
Is this an omission from the powers list, or a play test artifact that later became something else or was simply removed?
These were playtest characters that we put in the back of the book, I think a few of them have some errors like missing or misnamed powers and other leftovers from the development of the game. If (or when) I revisit the game the NPC's need to get another editing pass, as I recall they were included last minute as it was clear that at least a few sample characters needed to be included in the book.
I wish the book was perfect, but it's a homebrew and this genre is particularly hard to get all the details right. So whenever someone brings these things up I add notes to an errata doc.