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Very interesting. Gut reaction is OP, but I could see this working. Would like the wording to be that it shuffles itself into deck (that also shuffles the contents), meaning you have to draw it again to pull it off again.
I would make the contents protected from effect, then maybe combine it with Redoubter's idea of shuffling itself, that way you can't fill it with Daniel Angels (or something) then use cards like Darius's Decree to clear it out, then continue to fill it up.
You will need to have it protect contents so it can't be targeted by Shrine to Artemis. Making it go to set aside would actually make it easier to abuse it since it couldn't easily be targeted by opponents.
You could give the opponent the choice of which evil character to discard. Instead of "discard an evil character...", "opponent must discard an evil character..."