Serial Killer

The Serial Killer (SK) is a third-party role in the Mafia game, aligned with neither Town nor Mafia. The SK must survive to the end to be declared the winner, outwitting both the Town and Mafia (and any other roles). Is is therefore one of the most difficult roles in the game to win with.

Strategy
Conventional wisdom dictates that the SK should aim to lay low, avoiding suspicion by being helpful to the Town, but not a leader of the pack. Balancing this level of usefulness and activity successfully should result in the SK avoiding being both lynched and killed by the Mafia. However, staying too quiet will inevitably make someone suspicious, and as the numbers in a game dwindle, the remaining players could be able to puzzle out who the hidden SK is.

The SK must also balance the numbers of Town vs Mafia in the game, if possible - if too many of one side remain alive, it is most beneficial to the SK to kill members of that alignment to keep the game balanced and both sides focused on each other, rather than on the hunt for the SK.

Basically, it all comes down to a lot of luck.