Silverback Elder 3
Cast this and then cast more dorks? If I wanted modality or any one of these effects I would find a card with EtB triggers. The card that stands out most as a thing I would play over this in most situations is Cavalier of Thorns. Titan of Industry is another. As is Workshop Warcheif and Acidic Slime. This list is not a short one so we will stop it there. This is certainly a fine card but it is a bit big and dumb and rather unreliable. This is just another one of the many answers to the question "How do I lose to Doom Blade?" Basically I want my dig threatening things and my modal things to work fully without needing follow up support. This does have good power but it comes with too high a risk.
Combat Research 4
Lovely to have a third Curiosity for building around in singleton. The legend part probably won't crop up loads but it is a delightful buff to have on a precious aura-ed up dork. A build around sort of card but a powerful one and certainly one you could now support in a draft cube.
Impulse 10/10! (it is actually just a 7/10 card but...)
Lovely to see this back replacing turdy Anticipate and the art is divine too.
Ertai's Scorn 6
Pretty solid as far as the three mana options for hard counters go. This is top five of such things along with the scry one, the foretell one, the one with a stifle, and the surveil one. And most cubes support one such card at best so there is that.
Urza Assembles the Titans 1
Without planeswalkers this does nothing, and without good ones in the right places at the right times this card quickly goes from good value to dodgy to shocking. I really like this card but you can't be going round putting things like this in a cube.
Ertai Resurrected 7
Versatile doesn't even really cover it! This does it all. It is Disallow or Hero's Downfall on legs. That is five different things covering you for most situations. Once we get past the insane versatility we get to a pretty fair card. Yes, we have two three mana cards on the back of our 4 drop however the card draw for the opponent ensures this is just a one for one trade and the four mana price tag feels like it is coming out about right for a fine three mana spell and a 3/2 body in the mid to late game. So, is a fair but versatile card worth it? In just one colour then very much so. As a gold card I am less sure. I feel like you might want things to abuse this with like Narset or Crystal Shards before it is really looking worth it. It feels a bit like a Hostage Taker that has a much higher floor and a much lower ceiling which is really where you want to be as far as design goes. Lacking that tempting tempting raw power could well leave this dangerously low on play though.
Ghitu Amplifier 2
Sure, I might play this as a backup Kiln Fiend. Probably not though, in such decks the kicker is of little use and so I am more likely to play something with a little more innate power. There are a lot of dorks to chose from now with prowess like affects and you can never play that many of them due to needing to support that prowess!
Pixie Illusionist 2
Cheap support card with a selection of places that might consider it for a number of reasons but ultimately probably wont due to low power levels.
Crystal Grotto 4
What a nice little consistency card. I might play this in budget cubes.
Llanowar Stalker 4
Elves and green get themselves a Foundry Street Denizen. The dorks entering don't even have to colour match making this technically a strict upgrade! In practice this is a combo style all in beater and that is not something green usually does. They are more about cards and mana when comboing. Absolutely you can try and deploy this and then combo off behind it and do a load of damage. Or you could play cards like Ezuri and Allosurus Shepherd and have a good stand alone card that doesn't have to come down first and survive and does other useful things. Then when you combo off you can win with those good cards instead of a Willow Elf... (go on, look it up, it is a real card, and you thought Norwood Ranger was looking tired!) Overall this is fine, a fairly powerful card that likely will not get nearly as much play as the red counterpart.
Floriferous Vinewall 3
A floriferous name if you ask me. Mostly I want the consistency and attacking capability of a Sylvan Ranger over this. I am also probably pretty happy taking the lower hit rate of Satyr Wayfinder to get that attacking ability. The yard filling is generally a significant positive. If however I really didn't want to mill or I really wanted to search for specific non-basics, then sure, this will be the best dork for the job. Playable.
This does a lot and it is cheap. Can't think where I would ever want it, certainly not in any cube draft deck. Creature auras are just fundamentally dodgy and this does nothing to address those core issues. As an aside, paying mana to give haste also really takes away from the benefits of it.
Flowstone Infusion 6
This is a lovely new twist on an old classic Immolation. Broadly I think the change to a one turn effect instant from an aura is a win. It makes it an interesting combat trick as well as a better removal spell. In many ways this is a fancy Shock that mostly does what Shock does but is way way more interesting and quirky with some upsides and scaling that you have to pay for in consistency. This kills a bit more effectively than a Shock taking out the likes of pesky Adanto Vanguards. Getting face damage in with Infusion is a bit rougher as you need an unblocked 3 toughness dork and you then need them to not have an answer to it. Getting to do filthy things with Kari Zev however make me want to run this! I rate it higher than Disfigure in terms of power, it is just that red has so much more playable one mana removal than black that Disfigure seems more interesting.
Shadow Prophecy 3
This is a lot of card but it is not often what you are in the market for. Not many decks want raw card draw and not many decks have domain. Those that do have all the other options on card draw and likely don't want to pay life or have no tempo. There are cheaper ways to fill up the bin as well. That all being said, taking 2 cards from 5 and putting three cards in the bin for three mana is massive. That is some Dig Through Time Gifts Ungiven levels of juice.
Phyrexian Vivisector 1
Lol, look, it is a common that is better than Weatherlight Compleated! And it still isn't cube worthy. Awkward.
Knight of Dusk's Shadow 3
Just got that this is a harkening back to Black and White Knight. Very good. Well implemented. Shame this is just a fairly vanilla beater and thus not all that well suited to cube. Power level is fine but it just isn't the sort of card you want.
Battlefly Swarm 2
This might be stealth good. It gets in a bit and does annoying stuff but also just threatens to take out any attacker. Good as this looks it can't be cube worthy. Holding up mana for the activation on blocks is going to ruin this.
Shore Up 7
Probably better than Dive Down as a blue protection spell. Untap is nice and power lets this be a combat trick as well as a counterspell for removal. Other colours have been using cards like this in cube for a while now so perhaps blue should get on the band wagon. Some dorks that are worth protecting might be a good start....
Destroy Evil 1
I liked Valorous Stance and I probably like this more. Stance however is old now as far as spot removal goes and is a long way off the mark. It was cute rather than great even back when it was first released. Removal just needs to be reliable and the hit rate on this is low. Most one mana removal spells have it well beat for % of viable targets.
The Cruelty of Gix 1
Despise, Grim Tutor, Zombify. Relevantly better than Zombify in fact, more of a Reanimate without the life loss as you can target a dork in any bin, which combined with phase I gives some inbuilt synergy. Even so, this card is a bit of a mess. It is a lot of value and can even be mana positive for you. It is just all very slow and somewhat conditional. Read ahead is a big help here but I suspect it mostly just means people will be firing this off in phase III most of the time and doing so out of necessity. A five mana Despise is late in the day, the tempo loss is savage and there is a good chance you hit nothing. Phase II is also a tempo void and isn't all that impressive in cube. Even in combo cubes that is a bit slow to be tutoring things up usefully. In non combo cubes the value of a tutor is lowered, generally to the point where you don't play any as the cost of them outweighs the benefits and simple card quality cards are way way more efficient and well suited. Phase III isn't even very good, you have to have gotten a fatty in to a bin and kept in there. Most good cube fatties are five and six mana as it is so you are not even saving yourself much mana with phase three of this card that often. Plenty of things also disrupt yards now and they are not trivial to fill, certainly with the bigger cards you want to hit with this which you cannot just cast and naturally have die first. All in all this is a pretty big wiff of a card as far as cube is concerned.