Hey All, first post. Hello and all that goodness. I love the game.
Currently, I have all of the cards (core + all expansions). I've played Massing at Osgiliath 2x in a 2 player game and we were slaughtered. I decided to run it solo and was quite surprised. It went easier than just about any other quest I've tried for me.
Here is how it went down, in no particular order of importance. I'll offer my suggestions of why it worked.
Made a 50 card Solo (wasn't supposed to be) Spirit Deck. I'm an old school competitive card gamer so I always have the "tournament deck" mentality in mind even if I have no intention of playing the game in tournaments. With that, I run 3 Gandalf - which were huge later in the game (more later).
I say it wasn't supposed to be solo because I ran about 18 Lore cards but I never once drew the Songs of Wisdom so they were dead cards in my hand the whole game. I typically do that but run 3 solo heroes.
Heroes: Frodo (my favorite hero in the game) + Dunhere + Eowyn. Starting threat of 24, which is key to me smashing the deck.
Turn 1: If I remember correctly, pretty sure I played a West Road Traveler (switch locations ally) that gave me 2 Willpower.
Turn 1 Staging: This, other than my starting threat being so low set the stage for all the greatness. If this draw was any different, it may have been an entirely different game. I draw the Rangers of Ithilien followed by a relatively harmless encounter card (don't remember seeing an enemy so pretty sure it was a treachery. Rangers come to my side and add to Eowyn for questing. I leave Frodo behind to defend, along with Dunhere.
From there, I'll keep it short. Again, without lucky draws I'm sure the games could go 50/50 if not entirely in favor of the Massing at Osgiliath but I'll offer up the pattern and strategies. See if it might spark something and work for you.
Low starting threat, so low that Dunhere can kill everything that you set-up stage with before it becomes an issue. He kills the wolves before they engage, and Frodo is enough to hold off the 1 Threat Scouts. Even with an unlucky Shadow card, Frodo still defers damage to your threat (which is why he is my favorite hero period). By the time threat reaches 2-3 turns in (27ish), the Wolf Scouts are already dead from Dunhere (he kills them on turn 2). Other than that, the issue of "dont travel to West/East bank isn't a problem for a Spirit deck. Trackers and other allies along with Eowyn alone keep you ahead of the curve in the staging area. Dunhere causes massive problems for any low threat engaging ally and you never have to use him to defend (Frodo) or quest (Eowyn). 1 of 2 things happen pretty consistently - either the guys Dunhere doesn't handle in the staging area come out so early that your threat is still in the manageable high 20s to low 30s so they don't engage OR they come out so late game that you are on the final 2 quest cards.
I stored up so many resources that I had multiple Gandalf in hand. Back to back Gandalf was ready when the Witch King hit. Galadhrims Greeting makes short work of many of the "threat increases".
So in short (to long I know but the game is so much fun and I've stolen enough good advice on here that I thought I'd contribute), the pattern is
1. Low starting threat + cards like Gandalf and Galadhrims Greeting keeps the bad guys away.
2. A few lucky draws (hey its all random right?)
3. Dunhere controls the staging area.
4. Eowyn does a great job early to manage keeping threat even without having to commit other heroes (dunhere).
5. Spirit deck is super strong "quest phase" so late game stuff is handled.
6. Gandalf and tons of resources late game allows you to hand dump to deal with Witch King.
7. Starting heroes are everything. They make or break the game, not the cards. They determine how early things engage (journey to anduin as well - if that is the Hill Troll one). They also allow me to store resources for late game (like back to back Gandalf) because by themselves they handle the phases (Eowyn can control quest by herself, Frodo can defend by himself over and over since he won't die + greeting and its still in control and Dunhere kills stuff).
Enjoy and thanks!