Those familiar with my other thread, One Deck to Rule them All: Nightmare Edition , almost 1 year old now, have seen how Boromir can take on all the quests. Now we kick it up a notch, and build two decks entirely focused on him. Together the decks have risen above just beating any quest in nightmare mode. You can beat any quest in nightmare mode, while playing as if there were actually 3 players in the game . That means revealing 3 cards every round, and treating X as 3. Boromir becomes so strong that he effectively counts as a whole extra deck. And that's just for the very difficult quests like Carn Dum or Battle of the Five Armies. For some standard quests these two decks could probably handle 4 player mode.
There is an extensive writeup of the decks on RingsDB with strategy details. Here's the link:
http://ringsdb.com/fellowship/view/193/seastan-s-boromir-2-handed
I've also published a video of this pair of decks playing against Battle of Carn Dum in "3-player mode" so that you can see it in action: Link
Enjoy! Let me know what you think!