Mindscape Apparatus 2
Fun card but in practice never getting played over two mana alternatives. Sure, cost reduction of two or three sounds great but there are fewer and fewer spells that benefit from those larger reductions and even fewer still that you can afford to play. Flash helps this a lot and makes it something some control decks might consider but I do not see this being used in a combo deck which are the common places to see cost reducers. Regardless of where you try and play this, it being a four mana investment that does nothing by itself is going to be really hard to overcome. A can just about imagine an EDH deck having the time and support to make this do impressive things.
Malcator, Purity Overseer 3
Oh look, a golden Blade Splicer with a silly ceiling. In cube we can generally assume that we are not getting many extra EoT golems. Blade Splicer is great but take away first strike and add in gold and we are suddenly a long way from interesting. I'll play this happily in the right sort of deck but I am not sure what that is or if it even exists? Is it flicker based or artifact based? This might clear some hurdles but it very much falls at the being golden one. You need to be a whole lot better than the playable mark this hits.
Tyvar, Jubilant Brawler 2
Love a three mana walker but this is too narrow for drafting cube. The +1 is often irrelevant, it is only a mana if you have the right dork, it is often just vigilance if it manages to do anything at all. Equally the passive ability affects almost nothing in cube beyond mana dorks. The -2 is fine but a little risky and narrow. None of it is great on curve nor high tempo. It is only really value if you get to effectively -2 twice and does that sounds powerful or game breaking? Nope. There are some decks where this is good support but they are constructed only and few in number.
Kaya, Intangible Slayer 5
This isn't a cheap magic card! Hexproof is a big deal on a walker however, it means you basically need to kill it with combat. There are a few mass removal effects that hit walkers but not enough to be relied upon. It is the reverse, or the other half of The Wanderer and their ability being to not be attacked by more than one dork. Nice design, interested to see how they play. Both are a little scary as they limit interaction and might well be too polar to be fun. Also, killing a 6 loyalty walker in combat that can +2 or just -3 to answer something and get a 1/1 token copy of it! That is no easy feat and I suspect one we will not often see. Kaya is going to be a real challenge to race as well with that +2 ability draining for 3 a turn. All in all Kya is very hard to answer and very hard to beat. This you would hope for from a seven mana card. The 0 ability is odd, I am not sure why we are giving away scrys but sure. This is fine if you are not ready to kill your opponent yet but also do not need to stabilize the board either. All in all Kaya is very powerful and well rounded as far as a suite of abilities go. Her only downside is being a seven drop. Titan of Industry and Ugin the Spirit Dragon are it for cards above 6 mana in my cube and there are not all that many at six either. Kya looks great but the bar is so high for seven drops that I can barely see it! Judging if Kaya has what it takes to clear it is hard and needs testing. Statistically no, very unlikely to clear it.
Mirran Safehouse 3
Cute tool for some decks, most likely EDH gates decks, Dark Depths and other singleton land based combos. Not a powerful card nor an easy one to make use of but unique and serving a purpose.
Skrelv, Deflector Mite 7
A Giver of Runes that looks like it has more to offer but in practice is probably just a bit worse. Skrelv can't block, it has one less toughness, it can be Shattered, it costs life or mana to use, it doesn't prevent damage so does not help assist on blocking duty or against mass damage effects like Pyroclasm. Skrelv also only protects against coloured spells. All these things given up from Giver of Runes just for toxic? In a poison deck this is great, elsewhere it is almost a blank. It will be very rare to kill with poison and just Skrelv as the source of that. It is also unlikely that the cube will have that many more poison guys. Despite my very long list of ways this is worse than Giver of Runes Skrelv still likely gets play in cube. Cheap dorks are good, especially in white. Cheap dorks that have ongoing utility are really good. Being an artifact will likely be a perk as often as it is a downside. And then there will be those hero stories where the toxic does come up. Skrelv isn't broken but he is very suitable and powerful enough.
Glissa Sunslayer 7
First strike and deathtouch is a naughty combo. Very hard to block this and do anything other than be a chump. Further to that Glissa offers some serious value when she connects. We seem to be in a world now where the limited power of dorks that do nothing right away is well appreciated by design teams and as such we are getting absolute monsters like this. The power here is off the chart if removal cannot be found for it. Glissa can be some kind of Questing Beast, a Trygon Predator, a Thieving Magpie with punch. Much as I hate this kind of polar card that puts you behind if answered well and snowballs if not, doubly so when they are a cheap gold card, this just has too much power and utility to overlook I think. Three mana is not so much that you are very behind even when they find the optimal removal spell. It is certainly a lot less devastating than with four or five drops. Power wise this is a comfortable 8/10 card but I am dropping it to seven for being a cheap gold card. Like, I am always playing a Gix in my cube before this despite Gix having less raw power just because Gix is mono coloured.
Ezuri, Stalker of Spheres 1
Overcost, narrow, and gold. I like proliferate but I am not sure this is a card I want with or for such things.
The Filigree Sylex 6
Just a Ratchet Bomb with more. It seems pretty unlikely that this is going to that relevant with other oil counter effects and equally it seems like it will be super rare to fire this off for 10 damage. Overall then the most different thing this has going for it in cube is the legendary status! Ratchet bomb is a fine card, I use it to balance things out when it all gets a bit low to the ground and wide. We are right at the other end of the meta at present and so there are not balancing Ratchet Bombs in my cube either. When next we swing that way I'll toss this in and it will do good work for a couple of months and then no longer be necessary and the pendulum moves off in the other direction.
Soulless Jailer 2
Sideboard tool only really. Does far too little by itself to be a consideration for drafting cubes and maindecks.
Lukka, Bound to Ruin 5
A fine walker but in gold I fear this isn't enough. It compares really poorly to Torch of Defiance which is a better mana producer, a better source of value, and a more reliable removal tool. Lukka is fine, mana is great, making bodies is useful, and removal is grand. This is all topped off with some flexibility in costs. Lukka is about right power and utility wise to compete with the lower end mono coloured walkers in my cube but being gold at that point just rules it out.
Vraska, Betrayal's Sting 7
Vraska does what Lukka fails to do by being mono coloured and therefor of sufficient power to break into cube. Partly this is because black has some of the weakest 4 and 5 mana walkers going. Basically Vraska is Ob Nixilis Reignited but with some cute things going on. Being that little better than Ob is all it really takes when you are so similar. Both have effectively a +1 to draw a card and lose a life. Vraska nicely does hers with a proliferate for some cute scaling potential. Both can pay loyalty to answer a dork. Vraska costs one less loyalty to do so and gets around things like indestructible and on death triggers however does concede a treasure in the process. Overall I would say that is a decent upgrade. If desperate you could use one of your own dorks for ramp and fixing! Both have ults that are such a long way off that you are rarely ever seeing them. Drawing cards and killing stuff is just going to win games way before you get to the ult loyalties. Even so, if Vraska lives that long you can have some reasonable expectation of her being able to kill by herself with the ult thanks to the ability to proliferate the following turn. A fine thing to have on a walker that didn't need it to perform. The variable casting cost is really nice. It makes Vraska a fine five drop or a meaty six drop. It makes her a lot more splashable than Ob as well. Vraska is a great example of a card with relatively low power but great option density, synergy potential, and suitability. Ob has lasted a long time just on suitability as he has pretty poxy power by todays standards. Vraska is a long overdue and welcome replacement for him.