To be honest I just read the available roles and isn't that game literally broken by a mass-claim?
Private PM conversations are the heart of SEN mafia. It's pretty much guaranteed that to some degree some townies would form secret societies with other players, and this act naturally makes them more leery of uninvolved players, which makes them more likely to attempt deceit, etc etc. Honestly some of the regular players got so good at deceit anyone who knows that would outright reject the mere idea of mass roleclaims :3
SEN mafia has quite a lot of setups where VTs are absent, and there were plenty of times people attempted to facilitate massclaims by using a confirmed townie as a hub. Every single time enough players from all factions reject for the massclaim to fail to break the game.
Also SEN mafia rarely has open setups.
EDIT: Where the exact number of each role is known. Also we like to throw in roles with withheld powers (see Beguiler) or roles even not mentioned in the OP at all, and those usually have powers that are immensely handy for fakeclaiming
Like last game (that Resident Evil mafia I linked in the previous thread) I was Beguiler, and I got the same powers as Watcher, Cop (the RE version can only tell if a person's a zombie or not, and zombie's somewhat like cult) and 1 additional town action AND role PMs of all non-zombie roles in the game, in exchange for town having no VT and a whole bunch of good power roles, near the end pretty much everyone confirmed a townie role (including me) to the town vig, and I still lost