I mean... really it is a silly proposition that people are putting forth.
Really the only one that makes sense is me being a DayVig SK--which would be cool--but would require:
1. there to be a SK - possible given the pre-game info
2. mail-mi to come up with the role - possible but unlikely given no one else has thought of it before
3. me to think that claiming right out of the gates was the best way to do it and more important
4. not use a shot day1 and indicate that I am not using a shot today
5. the presence of a NK (ok, yes this could still hold true that if I use a Dayshot I lose my NK)
So there is the possibility. I think pretty unlikely off the bat. Yes the longer I stay alive (and other mafia/SK aren't flipped) the more likely something is fishy is up, but still drastically low.
Because for me to be doing what xeiron suggested would require me to claim w/o knowing if another player had said role. I get what xeiron is saying that I would basically be sacrificing myself for chaos and semi-IC status and 2 or 3 days of trying as hard as possible to not get my teammates lynched. All that sounds ok, but would require me to risk being counter claimed. Dayvigs aren't the most common role in the world, but I would say we have had 3-4 of them. Enough to make it a pretty big risk. Add in the threat of a normal vig--very common in RMm--and it would be extremely risky.
So yeah, I think that if I live and haven't proved myself over a series of days then suspicion might be justified. But this is day2 and I WILL NOT be intimidated into shooting if I do not think it is an opportune time to shoot. If you think lynching me is a good play instead then you must believe something very contrary to everything I just laid out and common sense.
So there probably is an SK: (1) It makes a lot of flavor sense. (2) The possibility was explicitly mentioned in the setup post. (3) Two people died last night. I know there are other explanations to (3), but an SK is (I'm guessing, new at mafia here) the most common one. But okay that would imply a day SK AND a night SK. I don't see why that's not possible (and I can justify it in flavor), but I have no idea if it would be done or not. So (3) is probably a point against there being a day SK.
Secondly, a Dayvig SK makes a lot of flavor sense. I could see any of the following characters be a third faction that can kill during the day:
(i) Elaida: Not Black Ajah but a real bitch and caused all kinds of problems for the "good guys". She was one of the biggest enemies that wasn't a darkfriend.
(ii) Children of the Light: Like a lord inquisitor or whatever. Not darkfriends (except for some infiltrators) but was another enemy to the good guys. And they did it under the symbol of the Light. They were a real problem and ever reader hated them with a passion.
(iii) Padan Fain/Mordeth: Night killing makes a lot more sense for him, but hey he could basically do whatever he wants. He had pretty singular powers and abilities.
Okay so I'm not trying to make a case. I just wanted to point out that it's possible. I don't have any idea whether or not it's likely in this setup because I don't really have any feeling of balancing roles or anything like that.
Though, if I recall the setup phrases it in the singular:
there may or may not be a third party role like a Serial Killer or Survivor.
Now you can argue it should be phrased this way regardless, but if you're writing this and you know there are multiple third-party roles, you may naturally pluralize things. So maybe only a single third party is the most likely case.
So, I'm thinking that two deaths during the night *probably* means a regular (night) Serial Killer. Which probably makes it less likely that's there's also a daytime serial killer.