Hmm, I wouldn't say any scenario in LOTR:TCG is easy but you should be able to succeed at Passage through Mirkwood. I'd suggest sticking to using two of the suggested single sphere core set decks using all four base set Gandalfs. Note that they aren't 50 card decks. Don't try to construct 50 card decks with just the single base set for two player coop play. Don't try the Tactics deck right off, certainly not for solo. Once you get experience with the game system then try multiple sphere decks.
What is bringing your heroes to ruin in Passage through Mirkwood? Death by wounds or threat problems? If there is a constant problem then either deck design or actual play decisions might need changing.
What is bringing your heroes to ruin in Passage through Mirkwood? Death by wounds or threat problems? If there is a constant problem then either deck design or actual play decisions might need changing.