I like the idea of "One Decks" but I also like playing thematically, so I'm making an attempt at One Deck Per Cycle where each deck is (for the most part) thematic for the quests in the cycle. I am playing normal mode, not nightmare. For my Shadows of Mirkwood Deck, see here:
https://ringsdb.com/decklist/view/23642/edgeofmirkwoodonedeckpercycleshadowsofmirkwood-1.0
This is a pretty standard dwarf swarm deck. Usually you want your opening hand to have at least one cheap dwarf so you can get Ori's ability going as early as possible. Other than that, King Under the Mountain really helps to get more dwarves out quickly. One thing I like about playing "one deck per cycle" is that I get to use cards like Ever My Heart Rises, which is basically useless outside the Dwarrowdelf cycle. Also Thalin really shines here with all of the low HP enemies.
For most of the scenarios in this cycle the piloting of this deck is quite similar: get dwarves on the table and repeat. If you manage to get Imladris Stargazer (thematic concession because I want the deck mining mechanic to actually work) out, you can carefully plan King Under the Mountain and Zigil Miner and Well-Equipped to great effect.
The only "edge of the knife" quest is Shadow and Flame, where your opening hand really needs to have a few 1 or 2 cost allies (Dwalin counts as long as you have another cheap dwarf to get to 5). On turn 1, don't play any allies. Then from turn 2 onward, try to resist the urge to play more than 1 ally per round; it's extremely important that you play one dwarf per turn so that Nori can keep your threat at 0 for as long as possible. If you pace yourself, you can eventually put all 27 damage on Durin's Bane in one turn so you can win quickly.