Yes.
I disagree with this. The serial killer and the mafia are enemies, they can't win together, so they are bound at some point to attack each other, helping the Town collaterally. We've seen 17 player games with 3 mafia and 1 SK in the past, it's not unbalanced. Of course the Town could have been crushed in this case, if they can't lynch a mafia before Day 5 (me) and if the SK doesn't kill a mafiosi, but it could have been different story if you did.
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