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
Rasaad yn Bashir 2.5
A bit more support for toughness matters archetypes which is always welcome. Certainly not the most powerful of those effects but playable none the less.
Gond's Gate 3
Another very powerful Gate support card that will significantly speed up the archetype as well as improving consistency.
Karlach, Fury of Avernus 3
Close to there but I think it is a little lacking to quite cross the line. Yes, if you have a board already then this is a powerful Relentless Assault on legs. If not then it it a bit of a Durkwood Boars. All good five drops seal the deal when you are ahead, it is about what they do when behind that sorts the chaff from the gems and this is in the wrong camp. Powerful but not in the right kinds of way.
Jan Jansen, Chaos Crafter 4
Lots of utility, lots of synergy, and a reasonably body to go with it. Narrow from artifact support requirement and three colours but certainly something I would at least consider for a selection of artifact leaning decks including some aristocrats builds. Oni Cult Anvil certainly likes this one!
Alaundo the Seer 1
Powerful effect but this not only needs to survive to untap, it rather needs to do this for multiple turns before any real advantage is to be had resulting in a card that is waaay too slow and risky
Shadowheart, Dark Justicar 1
Oh look, another card that is way too slow. Yes, the card draw is nice but it is wildly overkill for such things. You need the body to be worth having as well as the effect for a card like this to appeal and a four drop 3/4 dork really misses the mark on that one.
Cadira, Caller of the Small 3
How wholesome, we have rabbits now to rival squirrels as the cute in magic. Cadira is not all that powerful on average but she has some really impressive scaling that might well tempt you into running it in the really token heavy lists.
Minthara, Ruthless Soul 1
A bit pricy and slow to come online. Ward 1 isn't doing enough to protect your 4 mana 2/2. Sure, if this sticks around a couple of turns it should be able to do a lot of work but that really isn't something you can rely on and so is not worth that risk. There are better ways to buff your dorks, either on dorks or on harder to kill things as your lists desires.
Decent into Avernus 8
This gets out of hand very fast indeed. This is 20 damage in four upkeeps although I suspect games will be well over before then due to the insane mana this confers. This looks symmetrical but in practice it gives two advantages to the owner. The main one is simply getting first use on the mana offered which is a massive tempo lead. Going first in magic, especially in powerful formats, is a huge advantage as you get 1 mana to use before the opponent. This is giving twice that advantage (sort of). Secondly you are the red player and so you are able to capitalize best on a big old pile of face damage. There is a risk that this just ends up killing you but mostly I think it will kill the opponent. I think this will feel like Sulphuric Vortex felt in cubes 20 years ago. For those not playing cube 20 years ago Vortex was an absolute beating and resolving it was one of the most reliable ways to win a game. I don't love this card as I don't love putting such an intense time limit on a game. I also don't love the risk this has of giving your opponent a potential advantage. Even so, on raw power level and ability to win games this has to be good enough. For every game it costs you it should outright win many more for you. It might even be too good. Scary concerning card.
Mirror of Life Trapping 1
Not entirely sure what you would use this for or why. It doesn't do nothing but it might as well. There is little tempo or value to be had here and I can't even really spot an obvious synergy. I guess if this cost one or two you might play it in a creature light deck to enact a kind of extra summoning sickness...
Raggadragga, Goreguts Boss 4
Narrow but very powerful. Lots of stats itself and a massive boost to your mana dorks. Cubes do tend to have a lot of mana dorks as that is the powerful thing green decks do. That being said, they don't have enough to make this nuts, just OK, and at that point this is likely too narrow leaving this as a build around card, and if you are building around this when not your commander you don't have enough payoff for overloading on mana dorks. One to keep an eye on for when more things that empower mana dorks get printed.
Wyll, Blade of Frontiers 1
Not many good dice rolling cards out there and they are not the sort of cards I want to play with even when they are playable. If I wanted to roll dice there are plenty of shit games out there like Snakes and Ladders I could play. I play magic to avoid such nonsense. Hopefully I never play with Wyll...
Bane, Lord of Darkness 3
Pretty mediocre all told. You are going to run out of gas in hand to take advantage of the effect here very fast if you get to use it at all. It isn't even that impressive when you do given the general size of cube dorks. You might manage to turn a Sea Gate Oracle into a Glen Elandra or Whirler Rogue and get some tasty mana advantage but more likely is nothing at all. If they are really scared or fighting a pure tempo fight they can just have you draw cards as well giving too much agency to the opponent. The only good thing about this dork is indestructible and that isn't reliable enough. You can't consistently curve out with this as a vanilla 4 mana 5/2 is how you lose games. Very narrow and effectively dead much of the time all while not having that impressive of a ceiling.