Have you tried the jester out? If so how does he play?
My thoughts, I'd be interested to hear other opinions:
And does he automatically lose if evil wins three quests?
Presumably so since he can't fulfil his win criteria, therefore I presume he will want missions to succeed.
How many good an bad guys are in the game for each number of players?
The fact that the jester needs 3 missions to succeed means he should replace a good character.
Does he get to know the minions?
This is interesting. The minions might have a hard time if he did, but the Jester will have a hard time if he knows nothing. If we assume the Jester sees the missions then we have a character with all the info that Merlin has but whose aim is get killed rather than avoid getting killed so that might be interesting to play.
The trouble is I don't think it would be interesting for the minions - either Merlin could get able get away without saying much and the minions might be picking at random from the people who are obviously not the jester (the loyal servants have no motivation to cover for the jester so he might end up being obvious). Alternatively Merlin might e really obvious hoping that the spies will assume he is the jester.
Playing a jester who knows nothing would probably be like playing a loyal servant - you need missions to succeed and you need to pretend to be Merlin.