Quick Summary

I realized a revised content only One Deck may be possible with the mining archetype after clearing Carn Dum (in both NM and normal forms) and the Dreamchaser campaign with an earlier, not quite RCO, iteration. I then retooled the deck to make it more flexible for every challenge the revised quests could offer me. Anticipating that Mount Doom and Carn Dum (the doom quests, I suppose we could say) would be the biggest challenges, I began with those two, and at this point I wasn't keeping careful track of how many attempts it took to clear the quests. For every other quest, I counted. Here are the results:

Took 1 try for Passage through Mirkwood.
Took 1 try for Journey Down the Anduin.
Took 2 tries for Escape from Dol Guldur.
Took 1 try for The Oath.
Took 1 try for The Caves of Nibin-Dûm.

Took 1 try for Intruders in Chetwood.
Took 1 try for The Weather Hills.
Took 1 try for Deadmen's Dike.
Took 1 try for Wastes of Eriador.
Took 1 try for Escape from Mount Gram.
Took 1 try for Across the Ettenmoors.
Took 1 try for Treachery of Rhudaur.
Took about 4 tries for Battle of Carn Dum.
Took 1 try for The Dread Realm.

Took 4 tries for Voyage Across Belegaer.
Took 1 try for The Fate of Numenor.
Took 1 try for Raid on the Grey Havens.
Took 1 try for Flight of the Stormcaller.
Took 1 try for The Thing in the Depths.
Took 1 try for Temple of the Deceived.
Took 1 try for The Drowned Ruins.
Took 1 try for A Storm on Cobas Haven.
Took 1 try for The City of Corsairs.

Took 1 try for Journey Up the Anduin.
Took 1 try for Lost in Mirkwood.
Took 2 tries for King's Quest.
Took 1 try for The Withered Heath.
Took 1 try for Roam Across Rhovanion.
Took 1 try for Fire in the Night.
Took 1 try for Ghost of Framsburg.
Took 2 tries for Mount Gundabad.
Took 3 tries for Fate of Wilderland.

Took 1 try for A Shadow of the Past.
Took 1 try for A Knife in the Dark.
Took 1 try for Flight to the Ford.
Took 1 try for The Ring goes South.
Took 2 tries for Journey in the Dark.
Took 1 try for Breaking of the Fellowship.
Took 3 tries for The Uruk-Hai. Pursuit value was 22 to finish.
Took 1 try for Helm's Deep.
Took 1 try for Road to Isengard.
Took 1 try for Passage of the Marshes.
Took 1 try for Journey to the Crossroads.
Took 1 try for Shelob's Lair.
Took 1 try for The Passing of the Grey Company.
Took 1 try for The Siege of Gondor.
Took 1 try for The Battle of the Pelennor Fields.
Took 1 try for The Tower of Cirith Ungol.
Played The Black Gate Opens once, got 7 resource tokens.
Took about 15 tries to beat Mount Doom. Finished on round 9.

Piloting This Deck

Generally, begin with a mulligan target of either a Wizard Pipe or Bilbo Baggins. Elven-light is great to see early too, as are Zigil Miners. The miners help generate lots of resources and can hit Hidden Cache and Ered Luin Miner when needed. Glorfindel, who is great at riding Wild Stallions, is an awesome engine for making sure our hand doesn't fill up with Elven-light, as we will be playing this card frequently. Dáin Ironfoot's action allows us to selectively discard the cards that aren't immediately useful to us, and Elven-Light needs to be in the discard pile to pick up the ones that are. Because this deck is entirely capable of mining itself away, we have two copies of Will of the West, and it's not uncommon to use both of them after reaching the bottom of the deck.

Longer-form Card Justifications and RCO One Deck Musings

The RCO One Deck Challenge

The original challenge of building a One Deck is being able to take it, without changes, through each quest in the game, using the hardest available version of that quest, or playing both when there's a case to be made that a nightmare version isn't harder than the original, such as the Battle of Carn Dum. The first deck we see called a "One Deck" is Seastan's The One Deck, which is a Vilya deck, relying on pumping out strong allies to overcome all obstacles and starting with extremely strong heroes that let you take control of the game right off the bat. Since that time, the Vengeance of Mordor cycle came out, with very difficult quests and a contract that is even more powerful than Vilya, Bond of Friendship, which has made various mechanically distinct One Decks possible (see, for example, The 7 (and 1/2) Walkers, A Modern One Deck, and The BEARST Deck).

Each of these decks relies on cards that simply aren't available in the revised content pool, but they also have to beat a lot more quests, so the demands made of them are far greater than those made on an RCO One Deck. That means there may be more archetypes capable of defeating each RCO deck, besides the Vilya archetype, which has been done.

As far as campaign mode vs no campaign mode, in my opinion campaign mode usually makes the hardest quests easier, which isn't what I want to test in a One Deck, and there is simply so much variability in what one can choose and which boons and burdens can be earned that it makes standardizing the quests difficult. Thus, I chose not to play in campaign mode, but it is likely this deck could do everything in campaign mode, with the only possible difficulty beating Mount Doom on a timer and not having unique cards captured in Mount Gram.

The Quests

There are a select few quests to think about in terms of what one should pack in an RCO One Deck. Top of that list is Mount Doom. You need the ability to generate high willpower in your heroes for fortitude tests, and any allies you play should be really helpful so you're not unnecessarily raising your threat. It's the ultimate test of an RCO One Deck, as it really requires the most different sort of deck compared to any other quest.

Escape from Dol Guldur and The Uruk-Hai mandate that you can survive without one of your heroes.

Battle of Carn Dum requires that your deck be top tier, which, if you're attempting a One Deck challenge, is a necessity anyways.

The Weather Hills and Siege of Gondor are both helped immensely if you have some form of healing.

The Dread Realm and Shelob's Lair both benefit from some direct damage, but it's not necessary to beat either of them.

Passing of the Grey Company requires either some threat reduction or a very fast rush to the finish.

For each quest in the game, you will of course need a solid defensive strategy, good willpower, and the ability to defeat enemies.

Looking at my success rate, you may be tempted to think that Voyage Across Belegaer is a difficult quest for this deck. It's just swingy. I got extremely bad luck, revealing a Corsair Warship and another ship enemy, on top of the one that starts in play, within the first three rounds for my first three games of it, and I just couldn't take all the enemies and archery.

This is a 52-card deck. Isn't a 50-card deck always better?

No, it's not always better. Let's hash out some of my frustrations at the obsession of a 50-card deck. We can take a hypergeometric calculator to find the odds of drawing either Bilbo Baggins or Wizard Pipe, my mulligan targets, on the first round with no extra card draw. With Gandalf, we play with the top card face-up, so for our opening hand, we see 7 cards and then can decide to mulligan. If we do mulligan, we get a new set of 6 cards, then we draw during the resource phase, so we see 8 cards. With a 52-card deck, we have a ~45% chance of seeing one of our four mulligan targets in our first 7-card opening hand, and if we mulligan, we then have a ~50% chance of seeing it in that opening hand. This means we have a 72.4% chance of getting our mulligan target in our opening hand with no other card draw. If you run through the math with a 50-card deck, you have a 74.0% chance of drawing one of your targets. This means that, over the 78 games I played, I most likely had a single game where I didn't see Bilbo or a Pipe in my opening hand where I would have if I had cut the deck to 50 cards. That's a tiny hit in consistency.

A fun thought experiment: without the 50-card limit, what would be the optimal deck size? This would, of course, depend on the deck you build, but a perfectly consistent 7-card deck simply cannot build up to the heights that this one can. If you're playing with a limited pool (core only, for example), then certainly there simply aren't 50 cards that will help you, and cutting down to around 30 will result in a better deck, but there are a lot of powerful cards that allow you to search your deck and hit back against Sauron now, so a smaller deck isn't always better.

So what are the benefits of adding cards? For one, this deck runs through itself multiple times. Not every deck needs more than 50 cards, but in this one, I see every single card, and can generate resources to pay for every card that I need to with Zigil Miners, Hidden Caches, and Steward of Gondor. That means that I'm regularly playing two extra cards that a 50-card deck wouldn't. In the context of One Decks, I'm adding in a lot of tech cards to make the deck extremely flexible so it can take on any challenge, but not necessarily be hyper-optimized for every single quest. In a normal deck, I'd remove Sword-thain and Strider, but you'll see below why they're in there. On the other hand, I could cut some copies of uniques/one per hero cards, such as Gandalf's Staff, Narya, Wizard Pipe, and Bilbo Baggins, but these are so essential for the engine of the deck that cutting these to make a 50-card deck makes the deck less consistent, not more so. In a deck where you have to fit in a lot of tech cards, increasing the total deck size can make it more consistent so you have more copies of your key cards.

Why aren't other One Decks more than 50 cards then? Because having a 50-card deck is a requirement of nightmare Deadmen's Dike. That's not a restriction we face with the RCO One Deck.

Card Choices and Justifications

Beechbone is not essential, but he's very nice for a couple quests and he always makes a good Narya target.

Elrond is amazing. He can heal archery damage or other accumulated damage or provide condition removal, all in a single-card package. To play him, we can Wizard Pipe him to the top or rely on Stand and Fight, which can also be used for Beechbone, Faramir, or any previously-discarded ally.

Speaking of Faramir, he's very important for Mount Doom to boost willpower, and can do so twice with Narya around.
Glorfindel is amazing for letting me discard Elven-light as much as I need and just providing very solid stats where needed.

Wild Stallion is fantastic. If I were to do this again, I'd add another copy.

Celebrían's Stone and Windfola were added as Mount Doom tech, but each was useful, though not essential, in many other quests.

Gandalf's Staff is mainly used for shadow-discarding purposes. If you don't have an engaged enemy, get a resource or a card, but shadows can quickly ruin your game. You can even use it on Werewolves in Carn Dum (but not Thaurdir, unfortunately).

Steward of Gondor isn't actually essential to this deck. There are plenty of other resource generators, but it is useful for the hardest quests when I want to endlessly cycle Lords of the Eldar. More on that below.

I really went back on forth on whether to include Strider. It's a staple card for nightmare Escape from Mount Gram, but it's not at all essential for a non-nightmare playthrough. However, it really earned its keep in Mount Doom, where I was able to play it turn one and spend five rounds with 5 or fewer characters. Occasionally useful when it came up early in other scenarios too.

Sword-thain is more Mount Doom tech. I attached it to Glorfindel so he could commit to fortitude tests, which was extremely helpful. Also not bad for The Uruk-Hai, when only heroes can defend or attack against Ugluk, but most of the time I discarded it as soon as it came up.

Flame of Anor could be excellent at the right time, similar to Éowyn's ability. For Raid on the Grey Havens, I ended up with this card in hand and Glorfindel on top of my deck for the first round, so I was able to quest with Arwen and Gandalf, defend Sahir's Ravager with Dain, then ready Gandalf and give him 5 attack, allowing him to one-shot Sahir's Ravager, giving me control of the scenario. Also great for Ugluk or The Black Serpent.

Lords of the Eldar isn't a card I'd typically include in a mining deck. It's present as an emergency willpower boost for Mount Doom, but it ended up being quite useful many times, even though you can only boost Arwen, Glorfindel, and Elrond (if he's in play) with it. If you're out of cards and out of Will of the West, then you can play this to get a card on the bottom of your deck for Dáin Ironfoot to discard with his action, boosting his defense. After he discards it, play it again and discard it again. My record is playing it 12 times in one round (round 35 of my 36 rounds of Ghost of Framsburg): I played it normally once (1), Zigil miners discarded it twice (3), I used Wizard Pipe to get it in hand then discarded it with Arwen's ability and played it again (4), drew it with Elven-light and discarded it to ready Glorfindel after questing (5), Fram's Shade attacked me in the travel phase when I traveled to Cursed Tomb (8), Fram's Shade attacked me in the combat phase (11), and I either Narya'ed a Zigil Miner or had someone for Glorfindel to attack to get it back in my discard pile for the twelfth play. All for naught, as I certainly didn't want to defeat Fram's Shade before exploring Cursed Tomb, but when you have over 100 resourced piled up, why not?

Reforged could be useful, especially as Gandalf helps you play events all the time, but in practice there are few enough items in the deck that it was lackluster. It certainly could be nice when a shadow or a corsair forced me to discard an attachment, or when I really needed to boost Dain's defense but had to discard a Pipe to do so, but those instances are rare enough that if I had to cut a card, this would be my first choice.

Gather Information is just good for when you need a side quest. If out early, it can be helpful, but usually it's just to delay placing progress on the main quest. Double Back, on the other hand, was very nice for threat reduction.

Other RCO One Deck Candidates

I've already mentioned a Vilya deck capable of beating all the RCO quests. Here, I show that a mining deck can accomplish the task, and I believe a Noldor deck can also do so, as long as you use your Ent of Fangorn's quest action at the right time in Road to Isengard. It strikes me that each of these uses Arwen Undómiel. Yes, she's that good. Other decks may well accomplish the feat too. I'm not as familiar with Silvans, but there could be a way to tool a Silvan deck to defeat all the RCO quests. A Celeborn-Galadriel-Éowyn lineup, while not entirely thematic, would get you into quad-sphere territory, and might be flexible enough to handle everything. If you can build a deck to beat the two "doom quests", it'll have a decent shot. But for me, I'll leave it to others to explore the feasibility of other archetypes in becoming an RCO One Deck.