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
Dynaheir, Invoker Adept 2
An OK power level and some interesting abilities. Neither of which help it get anywhere near a cube slot.
Bhaal, Lord of Murder 4
This is OK, it is easy enough to make indestructible and at that point it is decent. A good amount of threat, safety, power, and utility. Even so, it is fairly comparable in power to the sorts of things you can do in one colour in the cube so being three of them makes me think this is going to be a rare sight in cubes.
You Look Upon the Terrasque 4
A very expensive Fog! This does let you inflict heavy damage in combat if things line up. Five mana open however and people tend to smell a rat... The pump ability is more interesting as it can do some pretty brutal things, either Wrathing your opponent, taking out key dorks, or inflicting heavy damage to face. Again, all conditionally. Modality and bonus pseudo modality on those modes helps with this being conditional but a five mana trick is going to be real hard to redeem. I give this a 4 because of power but in practice it feels like a 1/10 as soon as we are talking playability.
Illithid Harvester 2
Cute but rather slow. A five mana 4/4 that might turn turn dorks into vanilla 2/2s is not wildly exciting and the adventure adds less than most do. A perfectly playable card but neither very powerful nor that well suited. It has the potential to look good sometimes at least.
Jaheira's Respite 0
Like a Settle the Wreckage, but more expensive and instead of removing the threats you get lands... so pretty terrible. I want ramp sooner, and I want it unconditionally.
Naughtyboy Ship 7
This is pretty interesting as it fires on three different angles. A 5/5 flyer for 4 is quite a threat. Crew 3 is a significant cost but not a back breaking one at all here. This will win games just by being tough to kill while also being big and evasive much like Celestial Colonnade or Smuggler's Copter. There is then the graveyard disruption element which is usually minor, often irrelevant, but useful and typically quite rare to find on good playable cube cards. Lastly there is the Reanimation aspect which rather pushes the ceiling. One hit from this is likely to result in big value and tempo. You can exile your own graveyard too increasing the odds you get (useful) dorks back. Ship is playable if it isn't getting stuff back even if it is pretty dull and pretty fair. As soon as you threaten to get back something worth having the card gets pretty scary. There is a wiff of the Scarab God about it. There is also much more than just a wiff of Weatherlight although Ship eclipses that pretty comfortably being bigger, less restricted by heroic cards, and offering tempo on top of value returns. I don't think this is a bomb but I do think it has a very real chance of lasting in the cube. It might however just be a less impressive version of Skysovereign, Consul Flagship.
Robe of the Archamagi 0
Good scaling but all too conditional, low tempo, and generally wishful. Just play reliable safe card draw rather than risking the blowout or dead card nature of this.
Alora, Merry Thief 3
Cute support card for Cunning Evasion, ninja, and rogue decks. A bit weak on the body side of things and a little pricier than I would like for a three drop but fine in the right deck.
Monster Manual 5
Elvish Piper got a long awaited and significant upgrade. No-one enjoys having to pay 4 mana for a 1/1 and then waiting to see if it lives... This is faster acting, cheaper to use, and rather safer. It even gives you a nice little adventure to dig into the deck to find things to later put into play. Much as this is a cool card it is a bit of a build around. It is going to take a lot of activations from this to get your mana back unless you have a whole lot of fatties in your deck. It is only ramp if you are deploying things that are six or more mana which is where my curve pretty much ends in cube. Normal decks do not have the meat to justify running this, you might as well run Aether Vile and even that is a little narrow for cube despite the wildly more suitable cost and relation to the curve.
Tasha, the Witch Queen 2
This suffers from the same fate as Elminster in that you cannot reliably make a defensive dork for this on the turn you deploy it. Sure, if you get to untap with it and you happen to have exiled something big and relevant then it is incredibly powerful. Mostly that will not happen and you have just paid a lot of mana to cycle. Even with support you are struggling to get 3/3 demon tokens out of this.
Wilson, Refined Grizzly 2
Mostly this is still just a Grizzly Bears. Good fun and a boost to the bear tribe but despite the large amount of text it isn't very powerful, threatening or useful. Reminds me of that recent Kobald legend... Wilson is cool to equip I guess.
Korlessa, Scale Singer 2
Good dragon support card but value based which is not what the tribe needs. Red is also the base colour for most dragon stuff and so this will be awkward to fit in. A tribal only card that is only a maybe for a tribal list isn't very impressive.
Mahadi, Emporium Master 2
This is no Mayhem Devil. It isn't really even a Pitiless Plunderer or a Gadrak. It is very much one of those middlemen cards that needs support to do its thing but then needs something to be doing with the thing it does else what is the point? All told this is a bit slow and a bit narrow. The power is fine but where exactly am I playing this? Even 100 commander sacrifice decks will struggle to fit this in so 40 card decks have no chance.
Wizards of Thay 1
I do very much like the passive abilities here but when stuck on a Phantom Monster the card rather loses any bite it might have had. All just a bit costly and vulnerable when the myriad is blank text as it is in 1v1 play.
Bonecaller Cleric 2
Zombify on legs! This is low power but it is quite playable. It is an early proactive dork with a bit of late game utility and kick. You need to want specific things back from the bin and you need to be a deck that wants to apply pressure which leaves this with very few possible homes but for a low power card this isn't without use.