But it's a jailer, so if he decided to protect the weak cop then he can't perform his action. Also the weak cop can be vanillaised. He won't get a result that he was targeted and changed roles that night so he can have false positives is scum is lucky.
Let's put ourselves in scum's shoes:
Cop has claimed and there's presumably a projector alive. It's risky to attack the cop because they don't know what protector it is.
Let's say scum chooses not to attack the cop and jailor jails cop. Maybe best case scenario as scum now pretty much knows of jailor and can maybe deduce they can't protect the cop the next night.
Let's do the same except scum attacks cop. While the cop doesn't get a result they're in a tougher spot having lost a night kill. They also know of the jailor, but they've lost a night kill and are probably wary of trying to attack the cop again.
Finally we have scum not targeting cop and jailor targeting someone else. Worst of both worlds as jailor can protect someone else (possibly scum or nk target) and cop gets a result.
My main caveat is without a strongman scum find themselves in a very uncomfortable position because they either target cop risking hitting a very likely protection or they target someone else risking cop clearing more players.
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I'm viewing this sightly biased because a jailor/cop situation royally screwed up scum in Sorian's championship final game. Not in a "this is super op", but in a "this can be really powerful" way and recognizing that the uncertainty regarding nk had a big impact.
The game was semi open, basically as power roles claimed you could figure out what the remaining roles were and mafia by virtue of knowing their own roles knew what town had.
The game was 13:4 (17 players) and the roles were a town odd night cop, town jailor, mafia strongman and mafia watcher.
https://www.mafiauniverse.com/forums/threads/3255-Season-3-Final-Game-The-Koopa-Troop
Link to game, use thread marks to find day start and ends.
D1 ended with a town lynch, but N1 the cop was lucky to find scum and claimed the next day. That scum was also the strongman so scum entered the night with a claimed cop and no strongman. Instead of aiming for the cop (who can't do anything on even nights) they figured jailor would protect the cop and instead aim for the strongest townie who was leading town (and would end up being voted best player). The jailor however figured they would do something like that and also jailed that strong townie. The next day scum managed to lose a second scum to the lynch and now we arrive at N3. Scum is in a tough spot because the cop is able to use their check tonight, but the jailor is able to protect them too. Scum end up targeting a vanilla townie and again jailor was able to anticipate this and the cop is free to use their check and was able to hit scum. Town was able to lock the game mechanically and scum ended up conceding. The jailor was Sorian btw ;)
Different setup and there was a strongman here who just happened to die early. My point though is the uncertainty plays a big part because either result is bad for scum. Jailor is also a pretty powerful role for town because they can block a kill two ways so I feel like scum should have a counter.
Regarding the vanillaiser: the downside is that it's a delayed action and if they use it on N4 the cop can still get a result, the cop will just be vanilla on N5.