Narfi, Betrayer King 3
This is a pretty efficient recursive dork. Three mana for a 4/3 lord is cheap. You are not even colour tied so a mono red deck with enough mill and discard could play this. Much as Narfi is high powered and does a lot of things it is still a card that needs support and ideally a couple of forms. You want the lord to be relevant and you want the recursion to be relevant too. This means snow or zombie heavy decks with discard effects. If you just make a 5 mana 4/3 and hope to win by remaking it at 3 mana a go later down the line you are in for swift defeats. As such Narfi is too narrow for cube and will remain a constructed card even if he is one with a couple of potential homes.
Aegar, the Freezing Flame 3
This is pretty easy to trigger being a giant, red having loads of burn, and Izzet having loads of wizards. Despite this I can't see it making cubes. Gold cards need to be above and beyond and this isn't. It is easily disrupted and situational. This is powerful but it isn't really powerful and it isn't that playable. Feels like a tribal card mostly.
Firja's Retribution 2
Another saga in the series of very powerful overall effects that are too slow and reliant on the survival of a token creature to stand up on their own. This card is really impressive sometimes and laughed out of the room by a Mind Sculptor or Brazen Borrower. I might play this in tribal angels, I wouldn't risk it elsewhere.
Stalwart Valkyrie 1
Much as I am well into a 3/2 flier for 1W in white this is rarely a two drop. At that point I might as well play Serra Avenger. The normal casting cost for this is a disaster and so I don't hold out much hope for this needy vanilla beater.
Reidane, God of of the Worthy / Valkmira, Protector's Shield 8
Now this is quite the card. Thalia and Gaddock Teeg's deity offspring! Reidane is playable by herself which is a great start. The body is fine, it is relevant and hardy enough to justify the cost. The effects can be pretty brutal. The main one being that you buy two more turns before a Wrath is online. She is horrendous for planewalkers too. Theirs exclusively. Unlike Thalia Reidane doesn't interfere with your plays so you can happily flop out four mana walkers after her. Rude. Also finally a punisher for playing snow lands. Astrolabe was a free roll in a lot of cube decks due to how I allow snow lands, Reidane will give some pause for thought on such things. Reidane brings a nice amount of relevant disruption at just the right time and cost. She isn't broken but she is perfectly on theme and well suited to the task. She is going to give control decks fits and that is for the best. She is still fine against midrange and even aggro decks too. She gets involved in combat and will slow a bunch of their spells.
The Shield is rather narrower in application but can be devastating. Against a burn deck or a weenie deck it is utterly gutting the damage potential. All burn spells cost one more and do one less. Nice two mana Shock your Lightning Bolt has become...It also ruins little things like Rishadan Port, little utility effects that target just become pretty inefficient to use over and over again. It slows down the game so much for your opponent. The thing is that Reidane is something you want to play in aggressive decks like Thalia. In those you are less interested in slowing down the opponent than you are about killing them. It is nice in that it randomly shuts off a lot of combo kills that white is otherwise vulnerable too. Brain Freeze gets a lot more costly. Infinite Deceiver Exarchs are no longer sealing the deal etc. Mostly I see the Shield as a card that aggro white decks will occasionally get to ruin aggro red and combo decks with. I don't think you can run this card in control on the merits of the Shield alone. It is too varied in what it does and too gentle as far as disruption goes for a clunky four mana investment. Control decks want dramatic recovery tools this high up the curve rather than a slow dampener that could wind up looking like an overpriced Sun Droplet. This is a great card overall but it is not one with loads of homes, luckily the main one it has is a top tier cube archetype.
Draugr Thought-Thief 0
Fateseal or surveil is quite a lot of utility and disruption. I like the card a lot but without flash or being scaled down this is just not close to powerful enough to tangle in cube.
Jarl of the Abandoned 1
Don't be tricked into thinking this is good thanks to the perks it has, the downsides ruin it. It is a removal spell you generally need to use another thing to turn on turning a two for one into a two for two. One with bad cost efficiency and low relevance. It isn't value or tempo, it is just awkward and slow.
Runed Crown 1
Lovely, a build your own equipment. Neat flavourful little card. No good in draft and likely little use anywhere for now. Then 10 years down the line they will print some Rune of Eldrazi Conscription levels and suddenly there will be a new modern archetype!
The gold utility land cycle 3ish
I didn't appreciate this would be a cycle when the first one was spoiled. I cannot be bothered to essentially say the same thing repeatedly so these are getting bulk reviewed. They are far too slow and narrow to be good cube inclusions. They do however do some significant and fairly powerful things ensuring they broadly have a chance of winding up in some suitable constructed decks. We are not use to seeing such significant effects on lands as these. A lot of the cards seem to do multiple things which gives them increased chances of ticking synergy support boxes. If the unspoiled Rakdos or Orzhov options are noteworthy I'll write about them. Utility lands have been one of the most notable power creep recipients over the last few years and the MDFCs from Zen Rising have really pushed the bar on that front. There were already dual lands with dork modes, that sac to draw or that cycle. The Castle cycle from Throne was exceptional too. These lands are not as powerful nor as playable as the new bar for such things but they are still strong cards that I expect to see getting a lot of constructed action from cube to EDH to competitive formats. Some of these might even creep into legacy with lands decks being a thing there. All slow but all fairly low cost of inclusion for a fairly high relevance late game perk.
Ascendant Spirit 7
Looks like a white card to me although blue obviously needs it far more. Blue has done well for tempo cards in this set so it will be interesting to see if I can sensibly support a blue aggro archetype in cube yet. If so then this is a premium new addition. If not then this might just not have the homes to get any play. It is most akin to a Figure of Destiny. It curves a lot better and is arguably a better return on investment, although neither impress wildly on that front. It is all about scaling, options, and getting ahead of the tempo with these kinds of card. This is comfortably one of blues best one drop threats. They all need some mild support and so you can't easily play them all in a cohesive deck. Luckily this is one of the easiest to pair with any of the others. High powered card but one that might not last through no fault of it's own. Cards need homes to get play. Power helps forge homes certainly, as this will do, but depth is rather lacking in this area for blue, Spirit probably isn't the card that tips the archetype over the line.
Usher of the Fallen 7.5
What a lovely little 2/1 for one. This is very fair but is still decently better than a Savannah Lions. It provides a bit of a mana sink, some nice options, and a means to develop the board without over extending all while being basically as good of a cheap threat as you can find in white. This isn't broken by any means. Paying 1W for a 1/1 token isn't good tempo or really impressive value either. It just has a solid floor with some meaningful upside options.
In Search of Greatness 6
Well now isn't this a card!? There are two key things going on here that stop this from being a total bomb. The first is that it works from the CMC of other permanent cards so you can't just flop this down and make a free 3 drop the following turn. You need another thing as well. The second key thing to note is that you need exactsies on the CMC. It is not "or less" and thus giving free reign on free spells once you have something big down. It does make the card a fascinating build proposition like Birthing Pod. Trying to curve up with this and milk it for maximum mana returns seems really hard to pull off though. You have to be able to protect your curve the whole way up and pack a load of card quality and tutoring to help you have your curve to move up with. This is an Aether Vial kind of card but the counter adding aspect is either forced by using it or disrupted by opponent's remmoval. It can return absolutely filthy amounts of mana fairly cheaply but it is a little restrictive if you want it to work properly. The scry if you don't make a thing is actually pretty huge and makes this potentially cube worthy I think. The floor is Search for Azcanta floor and the ceiling is a better than a personal Mana Flare. The reason it is possibly cube worthy is that you really don't need it to cast things for you often for it to be great. Lets say your first play is this on turn two. Then you make some generic value three drop on the next turn after your pleasant "free" scry 1. On turn four if they didn't kill your three drop, perhaps it was an Eternal Witness getting back a sac land or a Blade Splicer or whatever. It is likely a chore to deal with it just to prevent the trigger but if they don't you can have an 8 mana turn on turn four. Not only is that more mana than a one drop ramp dork would provide in that time it comes in a big chunk allowing for a more substantial card to be deployed. A brace of a planeswalkers perhaps? A Thrun and an Armageddon? That is a massive swing and very plausible. Always having to choose the most expensive card is awkward and stops you just jamming a load of cards at two points on the curve into your deck. At least you tend to be winning when you have your big stuff in play so this is either doing work or you are not in need of it doing all that much. This is a really dangerous looking card despite the attempts to keep it fair. Fire of Reclamation and Wilderness Invention both wrecked havoc on standard, this is half the price.
Skemfar Avenger 3
Miara, Thorn of the Glade suddenly looks very weak. Not quite enough support for this to cut it in most draft cubes but a solid little tribal card that protects on a metric elves want.
Dwarven Reinforcements 2
Perhaps you play this in tribal, perhaps just cause all the dwarves are weak and you need to make up numbers rather than the conventional double scaling for cards that make two things of a tribe in tribal. Pretty sure this gets a 1/10 but I am blinded by my love of foretell.
Tundra Fumarole 4
This has some extreme tempo potential. When this effectively costs you 0 mana the card is a total bomb. At 1 mana it is very good. At two and three it is fine too so an OK floor. It is however quite hard to have this be 0 mana. You need to cast it with basics meaning you are mono or it is well past turn three. You then need to find a use for three colourless (snow) mana. That could be paying towards something great like a Glorybringer if you somehow also have another RR. It could just be playing colourless cards too like dropping down a Sword. I think this will not be broken often enough to make it worth playing over a card with a kinder floor. In the right place however this is a premium tempo removal card.