Just for clarification, is the Thug 'immune' to an attempted infection as well? One could read the discription either way.
the way it was intended is that if the person killed during the infection OR the subject of the infection are under active protection (by the guard or by being a thug with still metal to burn), then the infection fails.
so yes, the THUG would be immune to infection, unless their 'save' has been used already.
on a related note, if we are adding another player (which would help the village) a possibility to balance would be to make it less likely that the WW infection fails, by giving the head inquisitor multiple attempts at infection (with the same dynamic), of course he would still only have 1 infection, just that if it fails, he can try again the following night.
Also note that this infection is considerably weaker than the usual infection, because it cannot be used reactionary (when the head is at danger of being lynched) and it need to occur at night, together with a successful killing. so the inquisitors might want to plan the infection earlier than usual, or risk to lose it with the head inquisitor if he is lynched or shot. this exposes the new inquisitor to being scanned earlier.
Please don't allow the WW (except through infection) assume the roles of the traditional villager specialist. The Seer, Lurcher (guard), Coinshot (hunter), Auger (Undertaker), Oracle (Priest) and Gnat should be villager only (I added the Gnat since it would be a worthless role for the WW

).
We also have had the discussion in the past about having the priest. I think that the priest slows down the game since everyone waits on the priest to reveal themselves. I would much rather have a specialist that is either a villager or a WW and whose power is to mimic another player's power one time (the player would need to be alive at the time of the power use).
I had considered something like that initially, but then i had settled in having the "only villager" roles just for the seer and the guard/lurcher, which are the two "Core" roles associated to the village and already cannot be inquisitors/ww.
I guess the AUGUR (undertaker) could also be assigned to the village, although also consider that if we lock a role like the undertaker (relatively weak) in the village, it increases the chance of a more powerful role going to the ww.
I sort of like the random aspects of the powers, so it gives more unpredictability to the roles, but one more wouldn't make much of a diff (and they still can be recruited).
The COINSHOT/instakiller is less of a traditional hunter, as s/he only has the instakill, which is not necessarily helpful to the village as you (half-jokingly) mentioned above.
On a related line of thought, one other possibility would be to always make one of the Inquisitor a SEEKER. this is in line with the Mistborns world (one of the inquisitors main job is to seek out allomancers, and gives more of a purpose to the SMOKER, who tries to protect the allomancers. or simply impose that the seeker and smoker must be on opposite teams.
the ORACLE/priest i think is ok as is. first, he IS an Oracle, and the role fits well (i really do want to model the abilities to the metal power), second, in a largish game the oracle/priest question is probably best served not a the very beginning, but when the air has cleared a bit. Third, the option of using the ability in a covert way adds a tactical layer and leaves more operational room to the Oracle, so the requirement to come up with the question right away is less stringent, IMO.
the last point that you make is quite interesting, because the role I had in mind for the 18th player does in fact works something like that
as far as the Aluminum GNAT, the way Inquisitors are created is always through an Hemalurgic ritual, also before the game starts...
