You win if you survive to the endgame.
Each night you may kill someone.
You are bulletproof.
You investigate as 'survivor'.
You lose if the town wins. This supersedes your win condition.
You lose if the mafia wins. This supersedes your win condition.
The town cannot win while you live.
The mafia cannot endgame the town while you live.
Your role MAY change to Serial Killer at some point in the game.