Hearthpwn

Thanks, good to know you're finding success with this deck.

Depends on what kind of deck you want to play, and what cards you already have. If you have absolutely nothing, this deck is substantially cheaper. Also, do note that Darkest Hour may be affected by the recent Barnes nerf, though it shouldn't hit that deck too hard, at least compared to Big Priest.

There are quite a few different cards you could put in that slot. You could add some more removal, like Mortal Coil or Imp-losion. There are also a few tech cards that could be in there, such as Acidic Swamp Ooze. My decklist doesn't include Leeroy Jenkins or Doomguard, but you could put these back in for some added burst damage. Lastly, having a single board clear, such as Shadowflame or Demonwrath wouldn't be bad if you're facing a lot of aggro matchups.

If you just want a card that does about the same thing, Plot Twist probably has the closest function to the Soularium. I think the options I listed above are a bit better, though.

Thanks and good luck!

Regarding matchups, There are so many diverse decks archetypes in Wild right now, I don't know if I can list every single matchup. Instead, I'll name the matchups I find to be the most difficult for this deck:

I find Candlebeard + Togwaggle to be the strongest combination, as you can play the coin and immediately give any minion you play charge.  This usually results in a really quick victory, around turns 4-6, before the other deck can get ever going.

As I mentioned in my reply to Yurosaki below, there are times where Ultimate Infestation gets difficult to play.  However, it's usually fine to discard a card from playing UI if you already have drawn a few combo pieces, as its unlikely that a specific burned card is a remaining combo piece.  If you draw 5 and discard 1, you are far more likely to draw into your combo pieces than discard them.  There will still be games where UI can't be played, and that's fine given how powerful the tempo swing of UI is.  Against slow decks, I would consider keeping UI in the mulligan if you have the ramp (Nourish in particular) to play it early.  Against aggro, of course, it doesn't matter what you burn, as you don't need to combo to win anyway.

I don't like Greedy Sprite at all, and it's been abandoned from the popular Malygos Druid decklists as well.  The problem with Greedy Sprite is that its 3/1 body doesn't do anything once you have already reached 7 mana or so.  It's only benefit is that it can be pulled from Oaken Summons, but it's much better to put in a Oaken Summons target that has an actual impact during all stages of the game, such as Fandral or Tar Creeper.  Plus, Greedy Sprite's ramp effect is too slow due to it being a Deathrattle.  You have to play the Greedy Sprite, and then it has to die, and then you only get an empty mana crystal, so the effect is that you only get the mana ramp 2 turns later typically.  By that point, the ramp isn't as relevant anymore.

I don't foresee the new expansion having much of an impact on this, or any existing control or combo Druid deck in Wild.  The new Druid cards seem to be at a low power level, especially when compared to what is already available for Druids in the Wild format.  The one exception may be Ferocious Howl, which serves the same purpose as Branching Paths in providing card draw and armor gain.  One advantage that Ferocious Howl provides is that it costs 3 mana, which is far less contested than the 4-mana slot in these types of decks.  At the very least, I think Howl is better than Feral Rage, which was in an earlier version of this deck.

Great to hear you're having success with the deck.  I think one advantage this deck has over Malygos Druid (and I'm not saying this deck is better, just that it has certain advantages) is that the unique combo pieces (Ragnaros the Firelord, Carnivorous Cube, and Deathwing are better stand-alone cards than the unique combo cards of Malygos Druid, as the Malygos and 2 Moonfires don't have much impact on their own.  I suspect the reason that some players are struggling against Paladin with this deck is that they aren't playing the combo pieces by themselves.  In aggressive matchups, all you have to do is stabilize; you don't need the Aviana combo at all.  This deck has enough powerful late-game cards to grant victory against aggro even if some of the combo pieces get discarded by Deathwing (which most aggro deck can't deal with anyway).

I added Majordomo to my deck for my last game of the season.  It wasn't really necessary, but here it is.  Ragnaros even has his own New Year emote!

Congratulations on hitting Legend.

About Ultimate Infestation, I do agree that it can often be difficult to find an opportunity to play it.  Once you have drawn UI, you should be looking to empty your hand to a point where you can play it. If you can't empty your hand, it probably means you already have most of you combo; in that case, you can often afford to burn 1 or 2 cards, with the knowledge that it is unlikely that the cards you burn are specifically the remaining piece of your combo. It feels terrible when you do burn your combo, but this is a card game, and you have to play the probabilities.

I agree that Azure Drake is a logical replacement for UI, and the spell damage and the fact that you can't overdraw from the Drake poses some noticeable advantages.  This particular card replacement would require some playstyle adjustments, such as being more aggressive in drawing with Nourish as opposed to ramping.  Judging from your success with the deck, though, it seems you have that already figured out.

As others have mentioned here, this card would works best in a deck that only runs a small amount of powerful Beasts, such as Hadronox, that you want to resurrect.  Unfortunately, this causes a major issue with the card.  The Scarab Beetles summoned by Spreading Plague and Malfurion the Pestilent, are also Beasts.  So in order for this card to perform consistently, it has to be in a deck that omits two of the best defensive tools available to Druid.

It remains to be seen whether Witchwood Grizzly or other cards released in the set can mitigate that loss enough for this card to see play.

Because this is a combo deck, not a control deck based on value like Cubelock.  Your win condition is to assemble the combo pieces: Aviana, Kun the Forgotten King, Ragnaros the Firelord, Carnivorous Cube, a Faceless Manipulator, and Deathwing to kill the enemy hero in a single turn.  A second Cube does not enhance the combo in any way.  The reason two Faceless Manipulators are in the deck is for matchups like Druid, where dealing 32 damage in one turn may be insufficient due to armor gain.  Having a second Faceless increases the damage output of the combo to 48.  In other matchups, the extra Faceless can be used prior to the combo, to copy a minion such as Voidlord for tempo.

Note that the fact that there is only one Cube in the deck does not preclude you from playing it outside of the combo in aggro matchups.  Against aggressive decks, simply surviving and outlasting them is a win condition on its own.  In these matchups, Carnivorous Cube can be played on its own for a 4/6 body or on damaged or silenced Taunt minions such as the 1/5 Scarabs or Ironwood Golems.

I tested Baron Rivendare out against the AI, and it doesn't work.  Even if it did, there would be no point.  Because of board space, the maximum amount of Ragnaros you could summon with this combo would be 6, as the 7th spot would be occupied by Deathwing.  Two Faceless Manipulators on the Cube already provide the maximum amount of Ragnaros.

Thanks!  It's interesting how interesting non-competitive decks like yours can evolve into something much more consistent with the right support.  In addition to Carnivorous Cube reducing the number of combo pieces required when compared to Moat Lurker, I think another big difference is that Druid is a much better defensive class than it was in the past.

I designed this deck for a competitive environment, so I couldn't include Majordomo Executus in the actual decklist.  For fun and memes, though, Majordomo would be awesome.  The Ragnaros hero even gets his own special emotes for extra BM value!  Plus, it would certainly be extremely satisfying to beat your opponent with one of the worst cards in the game.