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
Shakedown Heavy 6.5
This is certainly a big boy for not that much mana. This is quite Browbeat like but regardless of what your opponent does you at least still have a 6/4 in play. They cannot afford to take much in the way of six to the face nor give away too many cards. This isn't always the threat you most want in the situation but regardless it is pretty threatening. You don't need to be applying pressure heavily as you do with cards like Browbeat as Shakedown Heavy is able to continue applying his own pressure. It is a pretty slow card as far as three mana 6 power evasive attackers go but it does seem quite good. It is a fantastic blocker and it is not trivial to remove. Power wise I think this is enough for cube but I suspect it may be a little linear to get all that much play. Cards that offer more options or more synergy might well edge this out of lists what with three drops being pretty abundant.
Illuminator Virtuoso 3
A nice little stealth heroic card. Good in decks that support such things and probably not elsewhere.
Toluz, Clever Conductor 6.5
Some immediate card selection on a body sufficient to ensure you are not losing tempo, and may well be gaining it. When Toluz dies you get cards back which will generally mean card advantage, sometimes a lot of it. Toluz is a kind of filler card that does a lot of things at fairly low cost. If it eats cheap removal then you get a nice two for one and can be happy about that. If they want to stop that value then they will have to use premium exile removal on Toluz and that will still be a one for one, will likely cost them more mana, and will leave them without premium exile quality removal for an actual threat you might deploy later in the game. The flexibility in casting will really help this out in cube. This is a bit too support filler card to merit being gold but given this can be mono blue, Esper, Dimir, and Azorius it is nearly as playable as Sea Gate Oracle, which in reality is the main competition for this guy. The upfront returns and clean low risk nature of Oracle probably results in it being the more played card but Toluz certainly wins the power and scaling side of things. Bit of a messy card but offering a good amount of stuff in the right sort of ways.
Out of the Way 2
Nice little sideboard tool.
Cemetery Tampering 1
Would love for this to be a viable mill tool or cheat out card. In practice getting 20 dorks in the bin in a 40 card deck is futile, you might as well just win with Thassa's Oracle at that point. Three cards is a substantial mill each turn which could empower a lot of yard synergies but at a three mana upfront cost it has basically no chance.
Topiary Stomper 7
This I rather like. Three is a lot for a Rampant Growth but it is become more acceptable as things are seeming to be getting more midrangy in cube. This has a lot going for it on top of being slow ramp. Obviously just being a 4/4 dork eventually is relevant but I do not think it will make up the lions share of the value. Seven lands is reasonably late on, you want a bit more return potential before that if you are paying 3 for a card that costs 2. Flicker effects seem like the obvious abuse for Stomper but there are plenty of synergies all over the place. You can use stomper to fight or to crew. It will trigger the likes of Guardian Project and The Great Henge, indeed it can reduce the cost of the latter should you wish instead. Stomper can be found with an Oath of Nissa or a Once Upon a Time which most land ramp spells cannot. Just having a body you can dump counters on or sacrifice to an edict is not worth nothing. Perhaps I am just using it to fuel Grist or Yawgmoth. A lot of these arguments do work for cards like Wood and Farhaven Elves but they are 1/1s which drastically reduces their potential power. Ultimately Topiary Stomper is a two for one with a lot of synergy and power potential while also being ramp. The thing most likely to hurt this in cube is actually the double green in the cost making it a bit more awkward in the four and five colour green decks.
Hypnotic Grifter 2
Three is just too much mana. I want to like this more what with it being a utility one drop in blue but it just isn't doing enough. This gets pretty tasty in a Training Grounds deck at least!
Unleash the Inferno 6
This is powerful, powerful enough I think to have a chance as a two colour gold card so there is a chance it is enough even at three. It is like a big Kolagahn's Command locked to the best two modes. It is Naturalize rather than Shatter which is nice, it is generally the case that this will have a target these days although often it will be a token of some sort, be it thopters, blood, clues, treasure, constructs, or food! Seven is certainly enough damage to take out most threats and leave enough left over to handle most of the Naturalize targets commonly seen. This is pretty broad instant speed removal with a good chance of being both tempo and a two for one. It is however still a removal spell and an expensive hard to cast one at that. If I had to play a Jund card in cube it would be this one but that doesn't mean I will end up doing so. Testing needs to go well for this.
Raffine's Informant 7
The power is low here but white aches for things like this and so it does have a very real chance of making the cut. With the likes of Land Tax and Tithe this as good as drawing a card on a 2/1 for two which is lovely. Just card quality on an OK tempo body is also fine. White has so many creature buff cards that any sized body is going to have use. Overall this seems to offer a bit too much to turn down for aggressive white strategies. I am not sure I would want this in midrange or control as the power is low. There are even some WX aggro decks which have access to better card selection where I might not run this and that makes it on the narrow side and combined with low power that might end its cube chances. Lovely to see more of this kind of thing for white even if I do not think it has the best chances in cube.
Brazen Upstart 2
This needs to die to do its thing which isn't a total disaster but it is rather the turn off on a Naya card. If it were cast with hybrid mana like Toluz, Clever Conductor then this would have a cube shot. The power is comfortably there but the colouring is too narrowing for what it is. Naya is also presently the worst three colour combination to be.
Rabble Rousing 1
This is likely only for EDH where you can go real big and wide with your token plans. In cube this will not have the support to do much in slower decks and will itself be too big and slow in the more aggressive decks. The hideaway in those will be less than impressive as well. Much as this isn't great 1v1 it is a lot of fun looking and can do some pretty big things.
Knockout Blow 2
Lifegain here makes this appealing as an anti red sideboard card. It may just be a bit fair to use a slot on when you could be going with thigs like Kor Firewalker and CoP: Red though. Either way, sideboard only card.
Shadow of Mortality 3
Another simpler tool to add to the Death's Shadow package. This doesn't jump around in size during combat making it a rules nightmare and that is quite welcome. It likely has some quirks and abuses of its own due to massive CMC. Dodging the likes of Unholy Heat and Fatal Push might make enticing in modern even if it is generally less powerful than Scourge of Skyclaves and the original Shadow. Narrow card but not without existing homes and a healthy chunk of power behind it. The main reason it is worse than a card like Death's Shadow is that you can deploy a weak Death's Shadow when at 12 life and then drop lower the following turn to empower it. This can only be deployed when you are already low making it not only a slower card but one that forces you to take bigger risks. I am somewhat expecting a deck to arise using things like this, Street Wraith, Gurmag Angler and that sort of thing that beats down and then has a backup plan of Erratic Explosion (or the new MH one that is far better) for loads.