Steam Workshop::TTT Traitorfier
The 'Traitorfier" let's you turn any silly old innocent or detective into a traitor, with the simple low price of harvesting traitor blood followed by a quick stab with an infused knife. If you can't find a Traitor's corpse to harvest blood from, you can also sacrifice 65 health to self infuse the knife, albeit on a longer cooldown until you can infect a victim.
While this tool has the face value application of increasing your team's size, there's a lot fun silly end game common sense scenarios you can disrupt/other chicanery to pull off with it. To balance such a tool (I think it'd be fun to play with for a seasonal update and rotate it out), it might be worth considering limiting purchases on a team basis to 2-3 a round at most. However, Demonic Possession wasn't capped and was a much more selfish thing, and yet didn't throw things too far out of balance of the standard flow.