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
Draconic Muralists 1
Expensive for a tutor but then considering it is on a 4/3 body it looks about as cheap as a tutor can get. Needing this to die does detract from the appeal and only finding dragons, especially for a green card, does make this rather too narrow for most things.
Candlekeep Inspiration 1
High potential ceiling but not an effect blue much cares for and needs setup on multiple axis.
Altar of Bhaal 7
This looks like it has a chance of unseating the long time cube staple Recurring Nightmare. While Nightmare was a once feared card of incredible reach and power it has rather fallen by the wayside in cube of late due to low tempo and vulnerability to things like graveyard disruption. Altar is a fraction more costly to use than Nightmare with that two mana upfront cost. It also can only be used once a turn, and the most notable drawback compared to Nightmare is that you cannot loop dorks. That probably matters less now as well as you mostly want to make tokens into fatties and then force the opponent to have to deal with the fatty rather than saccing it off again to the Altar. It does however stop you just getting abusive with the likes of Ravenous Chupacabra. It also stops you triggering on death effects which is annoying but it mostly reduces synergy potentials than raw base power. Altar is also rather easier to answer than Nightmare as it sits in play rather than hiding in hand. So with these many minor downsides compared to Nightmare what does Altar offer us as an upside? Just the adventure mode really but it is quite a big upside. It is fuel if you need it for the Altar. It is proactive and reasonable tempo and not even devoid of threat. It makes this card not simply dead weight in hand while the early tempo war rages. It isn't powerful but it turns your card from a luxury late game tool to a well rounded card. This is a long way from a bomb but I do kind of prefer the design and suitability of it for cube than I do Nightmare. Who knew a 4/1 menace for three could make such a difference to a card!
Undermountain Adventurer 2
Cool card with a good sum-of-parts element but ramp and value start to lack bite where this comes in on the curve.
Ancient Bronze Dragon 1
Too slow and conditional. Where is my immediate impact? My security against removal? I am not even into Sneak Attack effects with this... A seven drop with only a combat damage to player trigger that doesn't even look good when combined with a Sneak Attack is quite the achievement, and not in a good way.
Vexing Puzzlebox 2
This is quite fun and is one of the first cards I have seen that makes dice rolling less awful in magic. This has an OK floor and can be scaled up to do some scary things. The floor isn't good enough for cube and the ceiling requires too much build around from cards that are themselves a long way off cube viability. I might try this out for some fun but I cannot advise doing so if you are in the market to win games.
Wild Magic Surge 3
A kind of Chaos Warp that is cheaper but more inclined towards returning a problematic card. You might get lucky and hit the only/last artifact, enchantment, or planeswalker in a deck and have this be a very solid instant speed two mana Vindicate! You might also just two for one yourself, give them some free EtB triggers and simply not do what you want to do with your removal. Not unplayable but not the kind of card I like to play with unless I really have to.
Flash is lovely on your Banishing Light cards but I am not sure it is worth a whole extra mana (without cycling for 1 of course!) Wiping out all of the same things isn't making up the difference either in singleton. Yes, you can clear out a whole pile of tokens but you are likely down cards and mana if you do. It is situationally useful but rarely a thing which is getting you ahead. A fine card but not one that makes the cut anymore now that white has premium removal coming out the ears.
I see this and I think Colossus Hammer. Play this with the likes of Doran and Assault Formation and you have a very scary card indeed. It is a bit Tower Defence for that kind of deck but likely better and probably does enough to power up that style of deck a tier by itself. I don't think we will be seeing such things yet outside of the casual formats but it is now more one to watch.
Young Blue Dragon 4
Much as I love this card it is all very mana inefficient. It is competing with Mulldrifter and I am not sure it wins out. Yes, this card lets you have your cake and eat it but the cake here is old and dry. Neither mode is good returns on investment and so when you combine them you do not wind up with a great deal. At least both modes on Mulldrifter come closer to the mark on value for mana. I want to like this but I really can't see it packing sufficient punch to last.
The adventure is cute and decent value but it is very situational. It could win the game all by itself but equally it could never do anything. A super flanking 7 drop turdfrog is not the back end that makes up for the rarely useful front end.
Breath Weapon 2
Sounds like the weaponization of halitosis. This is a fine card but it isn't exciting or powerful or critically the best of this kind of effect and so I do not see it getting much cube action. Two damage isn't the sort of thing that kills a dragon anyway so not much of a boon. I would probably still be playing Pyroclasm in a dragon deck if I wanted a little two damage AoE spell.
Circle of the Land Druid 3
Much as I am a huge fan of Satyr Wayfinder the getting of land being an on death trigger mostly kills this card. When you want land you want it now so the time this would be most useful it is in fact not. I might well still run it in a self mill deck but I wouldn't ever run it in a more conventional setting like a would Wayfinder and that makes it entirely unsuitable for most cubes.
Basilisk Gate 2.5
I thought they were giving Wolf Run to gates as well as Cabal Coffers! Gate of Alexandria, Strip Gate, The Gate of Pendrel Vale, Mishra's Gateshop?! Then I saw this was sorcery speed and I clamed down again. This is fine. some utility for gates decks and most importantly yet more gates to reach that all important critical mass.
Sculpted Sunburst 3
A five mana Wrath that lets you both keep your best dorks or might let you keep one of your worst while they keep nothing. Interesting and very close on power level but sadly, when it comes to Wraths you generally just want the cheapest possible option and don't care about frills that might eek out tiny edges. This is playable but not really good enough.