Ok, so it may seem obvious, this is just to confirm.
The lvl 3 challenges in this game each have a requirement of "2 Watchmen Cards". Does this just mean cards that have the "Crisis 4" logo at the bottom, essentially cards from the Watchmen pack? I ask this because it's something that players should be aware of at the start of the game, but by the rules it looks like the challenge stack is hidden information. (granted this becomes obvious with multiple plays) Hence if a traitor wanted to sabotage the game they could go after all, or at least 9, of the watchmen cards and end up stumping the loyals on challenge 3.
A "Watchmen" card is a card from this Crossover Pack. If you let one person get all the Watchmen cards they are probably the traitor and you've already lost the game.