0 - unplayable in 40 card singleton
1 - effectively unplayable
2 - has low tier constructed decks it might go in
3 - has mid tier constructed decks it does go in
4 - pretty powerful stuff with several potential homes, able to perform well in lower powered cubes
5 - powerful stuff that is either just too narrow or has too many superior alternatives
6 - fringe cube worthy
7 - cube worthy
8 - cube staple
9 - unpowered cube bomb
10 - powered cube bomb
Jugan Defends the Temple // Remnant of the Rising Star 7
Much as I find the first parts of this saga wildly unimpressive it is quite a threat on the back end that really needs answering. Remnant will come to dominate a game pretty effectively. It will make all your dorks into rather more serious threats while acting as a partial mana sink and generally helping to provide good mana efficiency. It will give green some nice and generally unheard of action in the skies holding off those spirits and thopters and faeries! It will dominate the board whenever it is a 7/7 as well. I think for green Remnant is worth the wait and that has quite the drastic effect on the value of the saga. It means you are not leaning on the front half, you don't need it to do reliable, powerful, or appropriate things. Paying three mana for a Llanowar Elf would be a stretch to say the least if it was a significant contributor to the playability of the card. As soon as it is a free-be then it goes from being underwhelming to great. It starts to compare rather well to Llanowar Visionary. Phase 1 and 2 roughly add up to the body of Visionary and phase III the EtB card draw. Rather than just a card however you ensure you not only draw in to gas but you also cast it. This card helps set you up early and close out late. It is full of synergy, diversity, and power. I am somewhat expecting this to sit slightly above Nissa, Vastwood Seer and the Visionary in the cube. Not a bomb but a good rounded card that does a selection of desirable things.
Kumano Faces Kakkazan // Etchings of Kumano 7
Much as I poo-pooed the black saga that is remarkably similar (and likely has more power) I would say this has more of a chance in cube. This is largely down to how red likes to close out games with damage and how strong and prevalent aggro red decks are. This starts out as a bit of a ping which is direct damage and will help it to have some immediate relevance off the top late. It is low power but at least on-theme. Phase two can be devastating if you play something like a Kari Zev into it. It is conditional but it is high tempo and offers good synergy and scaling. Luckily it is also not a disaster should you wiff with it. Certainly you want to avoid that but you are getting just about enough card for your investment most of the time without it. The ultimate body is obviously pretty so-so but it applies pressure and works towards your goals. The static effect it has is what really pushes this card from unimpressive to playable. Exiling things is really powerful and shuts down loads of stuff. This can happily just sit in play and be a high priority to answer for your opponent adding to an already large number of important things to answer than only cost 1 mana like Lavamancer, Soul-Scar Mage, and Bomat Currier.
Invoke the Ancients 6
Much as I do not love investing overly in large tokens this is a pretty scary card. These will hold the fort or apply a lot of pressure as required. 8/10 of stats over 2 bodies with the ability to tailor them to the situation at hand seems all round good. You might lose one of them to a free bounce or flicker but that should still leave you in an OK position. I think the actual problem here is the quad green in the cost making this pretty much a mono coloured card and thus too narrow. If it were one or two green mana I suspect it would wind up in a number of the multicoloured green decks that are popular and high tier at present in cube.
March of Swirling Mists 2
Versatile but a bit aimless. Being neither a threat, value, or an answer, this stands little chance in cubes. Despite that I think this is a reasonable little spell and could well see it cropping in small numbers in places like standard.
Ninja's Kunai 3
A Lightning Bolt in colourless for three times the mana cost and needing a dork to equip then tap down. Power is not what we have here. Much as I mock this is cheap and direct. I can see this getting run in pauper cubes and being decent. Equally I can see it as a role filling support card in an equipment themed deck. It might not be good in most cubes but it would certainly be playable which is impressive in and of itself.
Iron Apprentice 3
More of these kinds of thing is nice, it is giving some real redundancy at the ideal CMC. To narrow and low power for drafting cubes but ideal to help the synergy decks interested in this sort of thing.
Ecologist's Terrarium 2
Cool support card but low power. I am more likely to play this as a Lay of the Land that puts an artifact into play than I am for the +1/+1 counter.
Eater of Virtue 7
This is a hard one to call as it is one of those side-grades on a card that has both an upside and a downside to it. This is mostly a Bonesplitter and that is a fine card, not exciting but pretty decent and playable. Eater can start to buff keywords as a game goes long. A Bonesplitter that gives any of those keywords is very good, and either one of the good ones or a couple of the less good ones and you have a pretty broken card. This is obviously something that often won't happen as your dorks don't die, or don't have the keywords, or are tokens, etc. The drawback however of exiling your dorks that do die while equipped with this is rather tedious in cube. It not only removes any on death triggers you might have but it also diminishes the power of the many cards that use stuff in the yard to delve or escape things as well as those that can recur stuff. I am wary of a cheap support card that has negative synergies, and not the low relevance kind. Power wise this offers a lot for rather little and so is likely worth some concessions. I imagine this is good enough for cube but might not play all that well and get cut on those grounds. It might also occupy too much of the same space Shadowspear does and not quite have enough demand to support both in which case Shadowspear is going to win out for being a more reliable and versatile card that makes games better.
Automated Artificer 2
Low low power but a cheap rock on legs might be the support card you are after in the odd exotic brew.
Tamiyo's Safekeeping 6
Keep a thing alive! This protects against most removal in cube but not all. Black has a number of things that give -X/-X that do not target and white always has Council's Judgement and exile based mass removal. It is also useful in some combats with the life being a nice little perk that helps push the power of the card that little bit. I like this and think it has a shot but I fear people are just not going to able to squeeze a card like this into many lists as it is not a threat, value, or an answer to a threat.
Commune with the Spirits 4
Premium card quality support card for any deck with a high enough enchantment count and not much good elsewhere. It might get a spot of play in decks with a few key enchantments as a way of increasing your odds on finding them and just having an extra land when you miss.
Careful Cultivation 3
The channel mode here is pretty interesting as it is instant speed and uncounterable ramp. The aura mode doesn't add much to the card sadly and it kind of needed to. Much as instant speed ramp is interesting it is not powerful enough in this case being a token and a two mana version of an abundant one drop card.
Voltage Surge 2
Efficient and even with some synergies. This will get a spot of play in the odd place but mostly Unholy Heat and Galvanic Blast will keep this out of lists.
Kami's Flare 4
This is pretty powerful and surprisingly close to the mark however red is getting overly full on non-face burn. The perk of this is face damage, and it is an overly conditional perk making this oddly unsuited and awkward. Certainly isn't threatening Searing Blaze!
Experimental Synthesizer 3
Sadly this isn't great without support. This isn't a cheap card to play ideally as you want to have sufficient mana left over to play the majority of things you might hit off the top with it. To use it a second time needs even more mana if you want good odds on a hit. If we are using this on turns five and seven it is starting to sounds pretty limp. I do love this card and want to play it for that Thoughtcast feeling! For that you need free ways to sac an artifact which are pretty abundant. Even so, it is then competing with the likes of Ichor Wellspring...
Virus Beetle 4
Cool, another Ravenous Rats, this one with artifact synergy. Playable but very fair.
Reckoner's Bargain 3
A number of better versions of this effect now on offer but nice to have the variation in perks. Black does like access to lifegain giving this a chance at some play.
Mnemonic Sphere 5
An artifact version of Hieroglyphic Illumination. Hard to fault useful cards with cheap cycling but this is probably too low tempo for most cubes. As soon as you start packing artifact synergies this jumps in power level but I have more than enough blue cantrip cards to want this just at face value, good though it is.
Mirrorshell Crab 2
Uncounterable Mana Leak with Stifle mode and big dumb dork mode. Nothing here is powerful at all but the card has a pretty extreme amount of modality! Doubt I am ever playing this but for a common this card packs a lot of action.
Disruption Protocol 2
Another Stoic Rebuttal kind of card, not as good as Metallic Rebuke but playable enough in the right place. More of a standard card than a cube or older format card where there are enough stand alone counters to fill out the ranks without having to lean on these narrower iterations.
Mothrider Patrol 2
Bad tapper but good Suntail Hawk...
Imperial Recovery Unit 2
If this were crew 1 it might have a shot. As it is there isn't quite enough power for the conditional nature of the card. White value is always nice to see though.