I don't have any ideas for allowing the Arsonist to meaningfully work against the Mafia, but here's an idea I had to allow the Arsonist to meaningfully work work with the Mafia against the Town:
The change:
While there is a living Arsonist in the game, any Town-aligned player visited by a member of the Mafia or Coven will become "lightly doused". Light dousing lacks the framing effect of a proper douse, but it does have these effects:
- If the Arsonist ignites, all "lightly doused" players will be ignited along with the properly doused players.
- If the Arsonist visits a "lightly doused" player, that player will be immediately killed in a single-target ignite.
This puts the Arsonist in the position of wanting to actively hunt the Mafia, while his passive ability grants the Mafia bonus kills.