With co-op and semi-cop already introduced, it sort of seems a natural flow from that point that there are traitor mechanics. Traitor mechanics are mechanics where one individual player can choose to change their allegiance to the rest of the group. Traitor mechanics are important to separate from semi-co-op, because a traitor needs to have had some reason to be in the cooperative group in the first place.
Usually, traitor mechanics are best deployed when there’s an incentive for players to succeed together, but also an incentive to succeed alone. This can be a challenging puzzle when you deal with it in a larger scale – you want to design things so the traitor is an option without it being a natural endgame. You can also use traitor mechanics as a way to introduce surprise and spice to an existing game structure (and it shows up in some co-op Legacy games, but I won’t mention which ones because that’d spoilery).
Note that a game with a traitor mechanic really isn’t too different from ‘a semi-co-op game.’ These arent pure descriptors of mechanical language as much as they are trying to be useful guides to what someone means when they mention a thing.
I tend to think that traitor mechanics want to be part of larger games – games like Archipelago and Battlestar Galactica, where if one player is a traitor, deducing that they are and routing around them still has enough game to it. That’s not to say they’re totally necessary to make traitor mechanics work – after all, you can view poker as a game based around a traitor mechanic, and so to our small game Pie Crimes.
I think myself, I’d avoid using the term traitor mechanic too broadly. It isn’t just the idea of competing, unsure teams like The Resistance – it’s about giving a player a reason and a choice to prioritise themselves over others. Dead of Winter does this by giving players secret goals – stockpiling medicine, for example – without necessarily making it break the whole group at large. This isn’t Betrayal At The House On The Hill either because it’s not like a player ever has to choose between competing rewards.
Mafia De Cuba and The Game Of Thrones board game.