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
Gavel of the Righteous 2
A slow but threatening equipment. This is too slow for aggressive decks and not at all want control decks want, nor combo or tempo for that matter. If you are playing this it is in a midrange deck and even there it is a little off colour. Midrange wants power and broad utility in the way a Sword of Fire and Ice might offer. Gavel is super linear. It is nicely cheap to get going and does get pretty out of hand at four counters or more. Indeed at more than four counters you can equip for free a lot of the time which is frightening tempo. You will rarely need that extra power or toughness when you already have +4/+4 and doublestrike. That is enough to turn even the lowliest of plant tokens into a beast of a threat. I do really like the utility of the equip modes. Sometimes you will really want to give a dork just a couple of extra stats so they can take out a walker or something and being able to do so for no mana and just a delay on your equipment growing is cool. This card is powerful and enticing to play with but on suitability terms it is probably never going to be the correct card to play in a 40 card list.
Agent's Toolkit 1
A cool card for sure and probably a useful support card in those decks that want as many counter types as possible if they ever become a thing. The power here however is low, it is a versatile utility tool with a slow return on investment and a relatively high mana cost to boot.
Cabaretti Confluence 1
Six mana three colour sorcery is killing this Confluence as well. This has some nice modes with reasonable meshing. Naturalize is always welcome on otherwise fine modal cards. Generating copies of your stuff and team buffs work nicely together and can provide plenty of tempo, threat and value. It is just all rather situational when you could be playing a game ending threat instead.
Aven Courier 1
Not useless but certainly no Thrumming Bird. This card is good for shield counters and it is good for spreading a diversity of buffs around dorks rather than focusing on one kind. Even so, there is no reasonable seeming build as yet where I would want to run this.
Misfortune Teller 2
This is nearly good but just doesn't get there. That one toughness is a bummer. You really want two triggers with this and that feels unlikely. At 1 trigger the power isn't there. The utility helps but not as much as it might what with Teller needing specific things in the bin to do its stuff. Teller is dying to way too much random and incidental stuff or trading with any random token in combat and that makes it a huge liability.
In Too Deep 7
This is basically a Fateful Absence. This is double coloured mana to cast and it can be undone if they have enchantment removal and wish to forgo the card draw. On the flip side, this is split second thus navigating around opposing trickery and it is effectively exile quality initially and in respects to on death triggers. Oh, and it's BLUE!! Black can kill enchantments, blue has a bunch of spot removal tools that resemble some decent white ones. The times, they are a changing! In Too Deep isn't broken by any means but it seems to be perfectly rounded playable removal and that likely makes it cube worthy. And it is Blue! I feel like these types of cards are mostly helping Izzet and Simic decks which previously lacked unconditional removal and relied on damage based removal, stealing and bouncing things. I am yet to see a powerful mono blue cube archetype in draft but cards like this certainly help that to become more of a possibility.
Rose Room Treasurer 2
A treasure back for the first two dorks to enter play each turn? Yes please! Sadly the Hill Giant looking body is a real turn off. Not much threat and plenty of vulnerability. Also far too late in the day for this kind of effect to really impress. A 1R cost 0/1 with this effect would be pretty special, even skipping the damage bit. At four all the vim is gone. You just can't play low threat high cost cards that don't stand up on their own, especially those that never go better than 1 for 1 against removal.
Obscura Confluence 3
All three modes are a little situational sadly. Raise Dead mode is the least situational and best value generator but it isn't amazing and doesn't scale well with itself. You really need to play this in combat with a bunch of dorks in play, and in the bin, then you can stand to get tempo and value. Sometimes this card will utterly dominate but too often it will be really awkward to play to any good effect. It does seem like one of the better three colour Confluences but a lot of that is down to being 4 mana instant and not because the effects are all that impressive. Not something I am excited to play at all even if it is probably just about fine.
Currency Converter 7
A handy little utility artifact that is playable by itself and scales up quite nicely with discard effects. Two mana for a loot is not great but it isn't bad either. You can afford to use it in the early and mid game if you need to. The final ability feels like it pushes this above Bag of Holding for general use and really helps offset any tempo loss from using the loot. If you make converter turn 1, loot away a land on turn 2 and then turn that into treasure on turn three you actually get to ramp yourself to 4 mana on turn three which is impressive utility on a looter. Making a 2/2 isn't quite the same early boost but it is still well worth having. It keeps the tempo of the card reasonable regardless and helps give you a wealth of options. I can see myself throwing this into any deck that already has discard effects, wants more discard effects, or simply a deck that craves a little more card quality. Converter isn't a bomb but it is playable in most decks, great in some, and should give good game play.
Mask of the Schemer 1
Some decent scaling and utility but ultimately a bit narrow and costly. It takes a lot to get going which is a risk you don't want or need to take making this fairly hard to justify playing.
Prosperous Partnership 6
Loving this. The floor is an over cost Krenko's Command style of card which isn't terrible. Those kinds of cards are played for the scaling rather than the baseline power. Assuming you are able to scale up your tokens a little then you will still have an OK card for your build regardless of the treasure side of things. As soon as you do make useful treasure the card jumps significantly in power. Ideally you can make this on turn three and get a treasure back right away allowing for a big follow up turn, perhaps empowering synergies. If you have any mana sinks this card will also break stalemates and board stalls pretty fast. If every dork is making you a third of a mana every turn it will not take all that long before you can do some oppressive things, be they making your Figure of Destiny an 8/8 or just sending a massive Fireball to the dome. Go wide Boros decks have been out performed by mono red and white decks for a while now but this is a pretty good reason to be in both. It may be a little narrow for cube but it is interesting, versatile, and reasonably powerful. I certainly look forward to playing with it and hope it performs well enough to remain in the cube. A fun card more than a nutty one but plenty of utility to help make up for that.
Master of Ceremonies 0
This is one of those cards that isn't at all good in 1v1 play. Poor body, poor tempo, and a symmetrical effect that is likely to benefit the opponent as much or more than you.
Killer Service 1
Cool support card I might play in a food deck even in a 1v1 setting. Unplayable without a lot of tokens you are happy to sacrifice for Rhinos and hardly all that exciting when you do. Your first Rhino is 5 mana effectively so you really need to be making at least 3 Rhino before this is good value, and even then that is contingent on sacing things of little to no value.
Life Insurance 2
A very powerful effect but on a five mana gold enchantment the potency is rather dimmed. This can kill you through the effect itself or simply through spending five mana to do nothing much right away. Certainly there are infinite combos with this using cards like Gravecrawler (plus sac outlet and say a Blood Artist) but in those sort of decks you are just going to be better off playing cheaper cards that do things by themselves. Ultimately this is interesting but very hard to use outside of EDH to any good effect.
Writ of Return 0
Big cipher cards are just asking for it. You really need not only an evasive dork but also one that is hard to answer and it is not often that you have Invisible Stalker to hand in cube. Even if you do have all that then you need good targets to recur. Frankly, just play Zombify or one of the many better cards.