Not that I like to bump dead threads, but I was bored one day (about 1 week ago) and logged in hit the who's online button and saw a random guest viewing this thread and decided to see if there was a 'splash' way to deal with horn filter. What about using
Grima, Servant of Another Master? Play him use his text to exert Gamling now he can't use the horn. Not only that but now you can use grima's other text to assign him somewhere that will hurt. Granted he is just a splash so he can squeeze into any shadow if you don't wanna deal with all the followers. Perhaps throw in that site that doesn't keeps followers from being transferred as well.
Idea is maybe use
Lurkers. Granted once you over exert Gambling you will have to finish the job that turn. But if you can swarm with all the twilight added from
lurkers and gambling can't use the text of the horn to pump everyone it might work. Not to mention
lurkers is already a powerful shadow and adding a few copies of Grima might not hurt it that much.
Another idea is Grima is a wounding gollum deck. Use Grima (retrieving him with
evil-smelling fens as needed) and then kill of companions with
They Stole It/Promise Keeping etc.... Can throw that site in that let's you exert a companion twice each time a follower is transferred (in fact throw that site in the lurker deck as well since when they transfer a follower they exert and that means more twilight for
Prowling Orc).
Anyway just a few ideas about
Grima, Servant of Another Master being a simple splash in a shadow to help combat against 'Horn Filter'. I guess you could also use him replay him with
Evil-Smelling Fens (or other means) and run pumps to have him win. Could also throw in
Saruman, Servant of the Eye to out exert to ensure Grima gets assigned.
NK