[ There will be a more concise and refined version of this only talking about the stuff you might want rather than talking about why you don't want certain things for your cube. It will be found on TrollTraderCards websit and I'll post a link when it is up. ]
Conspiracy is a far out set in terms of what to expect. Being aimed for draft and multiplayer purposed and not constructed play it has things ranging from the grossly over powered to stuff that doesn't really work properly. It also incorporates several mechanics and card types that require consideration as to whether to put them in cube that is based on more than just the cards power.
The three things from this set that would seem to fit under these special mechanics are "the monarch", conspiracies themselves, and the cards that have a "when you draft this" clause. The latter only really work in draft and as I do so many formats with my cube the effort of taking them in and out all the time sounds like it means they are not worth it for me. For those of you who exclusively draft cube or have the willingness to mirco-manage them I will include such cards in the review.
The conspiracies are very interesting and from what I recall would generally work in whatever format you were using with the cube. I never got round to collecting the ones from the first set that seemed interesting and as such I have never tested them. I likely will if I fancy something a bit new and exciting but I seem to think they didn't seem that balanced for cube with some being too mild even for a free effect while others seemed unreasonably good. While only some conspiracies are powerful, as they are all free in some respects there are cube formats and situations where all of them, new and old are playable. Even the ones not reviewed here could be used should you feel the need to be a bit more exotic.
The monarch is a new idea for this set and seems like it will translate into one on one cube fairly well. I assume it simply works that no one is the monarch until a card is played that makes someone the monarch. This means it won't be a major deal in cube but will add an interesting dynamic to some games where it does occur. Once the monarch is in play it seems someone will always be said monarch till that game is done. I really like the design in much the same way as planeswalkers are good. It will encourage attacks that might otherwise be unfavourable. The control player may take their turn to swing in with a man land simply to become the monarch where they would have preferred to pass with all their lands untapped. Drawing a card every turn at the end of your turn is a powerful thing that you cannot let stand for long else the game will get out of reach. There are some potential downsides to it as well though. It is a bit of a win more mechanic, when you dominate the board it will be easy to retain the monarch and still apply pressure meaning you won't run out of gas nor will you be that able to over extend. It also really punishes some archetypes that are creature light and cannot easily claim the title even when they are in a good position. A Phyrexian Arena is a decent enough cube card. One that draws you cards half a turn cycle quicker, causes you no pain and in immune to removal seems well worth 3 mana, probably more like 4.
Goad is a new mechanic that doesn't really work in heads up games as intended. Goad is a little like a reverse provoke or exactly like the effect of Norrit or Siren style cards. Forcing a guy to attack you is not that exciting, occasionally it will kill something small or a utility dork without a tap effect but you have to have a blocker for this to work. It is slow, situational and not all that powerful and as such I don't expect to see goad being worth much on a cube card. If any makes it to the cube the chances are the card would do so even without the goad on it!
Kaya, Ghost Assassin 5.5 - 6
First off we have a card with none of the set specific mechanics! The design on this card is delightful. Sarkhan the Mad was one of the most interesting planeswalkers but he never really got to see play so we could enjoy all his unique design perks. This was because he was go awful but Kaya looks a lot more playable than old Mad Sarkhan. The reason I am comparing these cards is because they are the only planeswalkers with no plus loyalty effects. Generally this means you have much more initial power, options and robustness but far less ongoing value or inevitability. Part of what makes Kaya so interesting is that despite not having a plus loyalty effect she has the capacity to reset her loyalty to the starting point of five. This means she does have the more conventional inevitability of planeswalkers with plus loyalty effects and good ways to use that loyalty.
Overall the 0 loyalty option for Kaya is one of the most versatile and one of the most effective protection mechanisms on a planeswalker. It can gain up to four loyalty and it can make Kaya completely immune to attacks and sorceries. If it is only one attacker you care about then you can exile that instead so neither you or Kaya take the attack. It is also useful for removing blockers should you wish to attack in. You can even do your own dorks to trigger EtB effects or protect them from sorceries. With all this taken into account the fact that you have to personally pay 2 life for the effect seems more than fair.
Both the -1 and -2 apply decent pressure, one to life totals and one to card advantage. Both are threatening and cannot just be left going rampant. While neither can be done repeatedly they can be done often enough that it is back breaking and both can be endlessly cycled with use of the first ability to reset loyalty. Over five turns you gain 6 and they lose 8 or over three turns you draw two, lose two life and they discard two. One of the two - loyalty effect should always be appropriate for a given situation. Either you are in a resource war and a 2 card swing is really savage or you are in a race and a 4 point life swing is significant. Even in a top deck stalemate two unblockable damage a turn is a threat. Part of what is so interesting about Kaya being able to do these infinite loops of her effects despite having no plus loyalty is that each subsequent effect use makes her a little easier to pick off. The first time you -2 or -1 her she is still relatively safe however the last time you do either without putting her in the bin she will be on just one loyalty. You have to chose between maximum efficiency or risk reduction.
While I am excited to play with this new exotic planeswalker I do also have some concerns about the card. Firstly it is a four mana Orzhov planeswalker. A colour pairing not overdone with archetypes yet fairly laden with good planeswalkers and other top end. Secondly the card is a poor tempo play. Beyond the ability to wave out their guys for a turn at a life cost Kaya cannot effect the board. She makes no tokens, doesn't buff anything, doesn't kill anything etc. Until the game is near over the change in life is of little consequence and cannot really be considered that much of a tempo thing. You either need to have a dominant early game with loads of dorks or great board control with spot and mass removal spells to play Kaya I think. You need to offset her inability to control the board by having a deck that does that well before you can really milk the huge value she offers in all other aspects of the game. While I think she is powerful enough for cube and probably the second best Orzhov planeswalker she still could easily be one one of those cards that doesn't see enough play to merit a cube slot.
Animus of Predation 7/10 (draft only)
A cool and interesting design for a card that is easily of enough power to play in cube but one that encourages too many things I am not into for me to really want one. Firstly, it is very easy to make this utterly nutty in the cube. A couple of guys that are going late because no one is in that archetype and this is like an indestructible lifelink flying haste no trouble. Firstly the draft only nature of this card is a bit of a turn off. Secondly, no matter how good you make it the Animus is still just a five mana dork. There are loads of those, and planeswalkers too. At best it is some kind of True-Name Nemesis, a card we don't need more of. At worst it is unplayable. Despite being far closer to the top end of that spectrum I am still not keen.
The main thing I have against this is that it encourages random drafting strategies. Perhaps you are some kind of Oath or Sneak Attack deck and really wanted that Ulamog that no one else wanted but then wait, stupid Animus has "hate" drafted away your card to make theirs better. Essentially Animus removes random cards from the draft and makes peoples decks worse. To make things even rougher this is all done open so that the players can foster some deep hatred for each other going into the games. True-Name Nemesis is already one of the top contenders for most unpopular cards and I fear that this Animus would be worse in cube.
Capital Punishment 0
Far too expensive for heads up magic where two votes is the norm.
Crown-Hunter Hireling 0
A five mana 4/4 with a conditional attack is pretty god awful. He has counter-synergy with the monarch mechanic which is an issue because that is the only reason you might play him. If you can be pretty assured you will stay the monarch then this card is powerful but a bit too top end for most red decks to be super hot for. If you lose the monarch then this guy is of no help getting it back and might cost you the game. I think that too few decks will be unable to challenge a monarchy that this card will generally be too much of a liability to risk playing. Interesting but no.
Illusion of Choice 2/10
This has got to be one of the most over powered cards in the actual intended conspiracy draft. It seems like it does some impressive things where there are enough vote cards going around. In cube this is just a way to get a 2 for 1 with Council's Judgement. This is as narrow as it gets but for a one blue instant that draws a card it doesn't stop it being playable. With much more voting stuff it might actually be quite reasonable in cube. Like a reactive Quicken!
Knight's of the Black Rose 1/10
Now this is a 5 mana 4/4 I can actually get behind. This one has positive synergy with the monarch mechanic. He punishes people for taking it from you and then helps you to get it back if they do. This is a five mana 4/4 with a built in card draw and then either a mini Siege Rhino effect or a free Dark Confidant. It is quite slow and midrange but it is very powerful indeed. Until we saw some 4 CMC monarch cards I quite liked this and had some hope for it in the cube but being 5 mana and gold makes this too clunky comparatively.
Summoner's Bond - very good
Good design and a very powerful effect. For cube this is somewhat above the curve. It is a completely free card for one. It is a completely free Tutor in the right deck and this is what makes it probably too dangerous. Ornithopter does not need to come with a free Ravager to be good enough. You can link any two cards that have synergy with each other or that are just really good all rounders with high power level and Summoner's Bond is the total business. You have good odds on seeing one of two cads in a typical game and so bingo, free top quality bonus card for little cost. In weaker cubes with lower counts of playables the card will be a little harder to pickup as it doesn't take the place of a potentially weak card in your deck. In my cube, even with my stupid high land count, there is such a high playability rate that this would be first pickable.
Natural Unity - incredibly limited but not without use
This effect is narrow as well as relatively low impact. This is not worth a card slot in your draft, you probably only take this when you have no picks and nothing worth hate drafting in a pack. There are some cards this would have fun synergy with but this just isn't worth a card slot for what it does. This is pretty much the same story for all the single creature affecting conspiracies.
Hold the Perimeter - weak and silly
Lovely design for a multiplayer card. For a heads up game this is doing far too little to be worth the card slot. Certainly there are some applications for having a free dork in play at the start of the game, even if it can't attack but those are too narrow for any sort of drafting cube.
Paliano Vanguard 6.5/10 (draft only)
While wordy and clumsy this is a really cool card that unlike the Animus works nicely in a draft. This dork is the lord of anything you want it to be a lord of. Being a white weenie card this will broadly be humans, occasionally soldiers but costing only 1W does make it a viable splash for some other tribal lordship. Great card for a drafting cube with a tribal theme. Basically every tribal synergy card I have is no longer in the cube as they were too narrow to draft but there is still a reasonable quantity of non-synergy tribal cards for which a two drop lord would be juicy. Although only practical when used in drafts this card offers enough to be viable in most cubes and will really shine in the more dedicated tribal ones. As you have to exile a card of a type you are playing odds on it is hurting you more than it is randomly hurting another drafter. It brings a new dynamic of choice to a draft while being an otherwise fair and broadly playable card.
Queen Marchesa 3.5/10
I have been burned by Mardu cards before so I approach this one with much caution. On paper this card is pretty nuts, certainly a whole lot more so than Butcher of the Horde! As with Knights of the Black Rose this is a card that has synergy with the monarch. A 3/3 haste deathtouch for 4 isn't bad, you can use it offensively or defensively to reasonable effect. Drawing a guaranteed card off the back of that is huge. You do risk giving the perk away to your opponent but then Marchesa gets really good at getting it back. You would certainly rather be the monarch then getting free 1/1 haste deathtouch tokens but it greatly offsets the risk of losing it. To get ahead they really need to kill her and deal you some combat damage which is a fairly big ask. The Queen should push on several fronts and be quite the pain. Despite all this I don't expect her to get any play just because of her awkward three colour pairing. I'll try her out but my expecations are pretty much zero for her.
Sovereign's Realm - ranging from totally overpowered to fine
This card is a bit too bonkers for the cube! Turn one this with Fastbond seems unreasonable. Even just cards like Exploration and Oracle of Mul Daya make this pretty nutty. Without the specific things that abuse it you are trying to just build a deck of the most powerful things. This means if you don't get it early in the draft you won't have setup well enough to abuse it. Often the cost of two cards will be too great to offset playing whatever you want. If you do get it early then you will suddenly be the most annoying person at the table just hovering up everyone else's juice! While very interesting this card seems a bit too random and swingy to be fun and balanced in the cube setting, certainly not for very long!
Archdemon of Paliano 0
Not really powerful enough to offset the drawback. In cube you can often be relying on late picks no one else wants tabling and Archdemon ruins that plan. Picked early in a booster he is a total liability too. I am not sure how good a 4 mana 5/4 flier would be in cube anyway so no real need to examine this trainwreak much further.
Arcane Savant 7-8/10 depending on support (draft only)
Certainly powerful enough for cube but awkward it its way and far too random and swingy for my liking. Get this with Cruel Ultimatum and that isn't even in the realms of cube fair. It will never be bad, it is decent value even when you are only playing a 2 CMC card with it. I will happily take a 5 mana 3/3 that casts a Lightning Helix for my blue deck thanks! Having this in a cube greatly improves the value of cards like Cruel Ultimatum or Time Stretch but I think that is a trap. At its best this card is far too powerful and not that fun but when you have to construct some sort of Battlemage with it I think it is very cool. It has a preemptive Wish style effect where you can draft some (off colour) cards that are good against the various matchups and then exile that card for your Savant. Only good in drafting and perhaps a bit too good to be fun so I am wary of this card but it is also interesting and cool enough that I want to play with it as well.
Assemble the Rank and File - super narrow
Nope, a conditional 2/2 is not worth a card even if you don't have to include it, draw it or cast it. Just having to pick this card and not having the option on another random cube card is far too much of a cost to pay to have this effect in your deck. Even if you are a zombie deck. Awful. In non-singleton cubes it might be a little less awful. Certainly you can combo it with a recursive dork and a sac outlet even in the singleton cubes but this is again, at the far end of narrow. Cool card design but unlikely to be seen doing much in cubes.
Thorn of the Black Rose 4/10
This is surprisingly comparable to Graveborn Muse. A 1/3 deathtouch scales better into the late game and is a better defensive tool. These are things you likely want when you are tying to protect your monarchy and use your extra cards. The card draw from Thorn is not tied to the body nor does it cause you pain as with Graveborn Muse. Thorn should always be a two for one right away as it will draw a card then force them to attack into it and trade. The risk with Muse is losing tempo when they instantly kill it with removal or losing too much life and dying too it drawing you more cards than you can play! Thorn has neither of these drawbacks but does risk your opponent becoming the monarch and drawing free cards. I think that makes this card narrower as you have to carefully consider how you are using it but I think it is still probably just strong enough for the cube. I like it more than I like a Phyrexian Arena, it may be too risky to claim its place however.
Ballot Broker 0
Too expensive, narrow and vanilla to be good even if we had a whole load more good vote cards join the cube.
Protector of the Throne 1/10
This is a really elegant card and something that white would love to be good. Sadly I fear this card has way too low stats to be worth a six mana price tag. Five is not enough health to be an exciting barrier to damage nor will it hold off that much extra pressure from creatures. This does provide card advantage which is rare in white on top of some protection for both you and your monarchy but it is just painfully small for a giant!
Custodi Lich 6/10
This looks like a pretty brutal card that can get out of hand. Not only is it a 3 for one when you make it the Lich also has some really serious swing potential when regaining a lost monarchy. There has always been a bit of a place for a good Edict on a stick in the cube because of Recurring Nightmare and how sacrifice gets around most of the top end protection mechanisms. Gatekeeper of Malakir saw reasonable play but didn't have the desired interactions to be a mainstay in the cube. This is a lot higher up the curve with is a bit of a problem for the scaling of Edict effects but it does come with card draw, potentially ongoing, and a 4/2 body. I think black has the tools to abuse this and so I see it being one of the more commonly used monarch makers used in cube. Cards that can give you monarch before combat such as Thorn of the Black Rose work very nicely with this card too should you have lost monarch somehow.
Hired Heist - underwhelming at best
Much as I like this it falls into the problem as the rest of the cycle. Simply too narrow to be worth the card slot. Some nice mind game potential, decent scaling with evasion creatures. Quite a lot better than the zombie generator which in turn is quite significantly better than the +1/+1 counter giver. I like the things this card does and so I can imagine it is one of the ones I would be more inclined to throw in to the cube. It certainly isn't as random or damaging as some of the other more obviously powerful ones are at least.
Throne Warden 0
Narrow, overly vanilla and not even that powerful.
Wings of the Guard 1/10
Pretty comparable to Stormfront Pegasus all round. I think I prefer a 2/1 all the time and it is hardly a cube powerhouse! Melee does not carry over in an exciting capacity to cube.
Adriana, Captain of the Guard 0
Deceptively bad. Like a Glorious Anthem only when you are attacking on an over cost do nothing vanilla body. Remeniscent of Marton Stromgald should you be in an 8 on 8 draft but in heads up this is the weakness.
Recruiter of the Guard 4/10
Functionally very comparable to Imperial Recruiter or even Fierce Empath, Goblin Matron, Trinket Mage or any other 3 drop dork that Tutors up a thing. Non-green (non-black) creature tutoring is quite exciting in itself as it opens up a lot of possibilities within the colour and existing archetypes. Overall I think Imperial Recruiter gets more things in the cube but Recruiter of the Guard feels like it has more homes than Imperial which is almost exclusively Splinter Twin lists. The card is far from over powered, you are playing a restricted Eladamri's Call / even more restricted Demonic Tutor for 2 colourless mana and then getting a free 1/1 for W into the deal. This puts it in the same sort of power level as a Reclamation Sage or Fierce Empath. The tempo is low and the value is mild at best. You have to want to tutor specific things up before this is a good card. It will certainly still get cube play but I expect people to get a bit carried away with this card simply because Imperial is so rare and valuable.
Confiscate Riches 1/10
So this is either a Time Stretch or a Time Walk plus a Confiscate. You can only sensibly not take the Time Walk option yourself if they have previously stolen something of yours which gives it minor utility. If they have a game ending bomb in play they will elect to eat the Time Stretch and hope you don't find an answer. If they have nothing then they will let you have some kind of token or land. It will be pretty brutal but it will never be as brutal as a nine mana card should be. This should win the game and it really doesn't in heads up. The only time I expect to see this getting use is when you have ways to cast it for free, then you have unfair value regardless of the game state!
Keeper of the Keys 0
While better than the red 5 mana 4/4 that gives you the monarchy I like this less. Blue doesn't need ways to draw cards, especially five mana sorcery speed ones that risk your opponent getting them instead of you. Give me a Future Sight or a Mulldrfiter over this, hell, give me a Honden of the Seeing Winds or whatever it is called! I don't think I actually mean that last one but you get the point. Blue isn't the best at stalemating a board and it is the best at drawing cards. Blue is not the colour for playing the game of monarchs.
Leovold, Emissary of Trest 2/10
Really hard to know what to make of this. Certainly a whole lot of power for the mana but does it work well together and then does it go in enough decks? Three colour cards not only have to be significantly above the curve but they also need to slot into a common and powerful existing archetype. Sultai isn't as rare as Mardu by a long shot but it isn't super common either. His first ability is a bit of a random hoser, some decks it will do nothing to at all and others it will be a royal pain for. The second makes it unprofitable to use spot removal or other interactive effects with your stuff. This is good against most decks but not all. It either means you are eating mass removal, getting your Leovold killed sharpish and them just eating the 2 for 1 or they are going to just cast dorks at you and kill you while ignoring your board. A 3/3 for 3 isn't bad stats but it isn't doing a lot without any combat abilities. Leovold gives too much control over his power to your opponents and has too bland of a body to make up for it. As a 3 colour card I can't see this getting close to enough play in cube. Good cards have an immediate impact on the game which this doesn't really. Even with his lack of cohesive design he is of enough power to be played in cube, just one of the many that wind up too narrow.
Entourage of Trest 0
I don't see this one much either. Certainly a lot better than Kavu Climber but green isn't great at stopping things getting through with zero removal, zero spell control and pathetic flying prowess. Green also has cheaper or more powerful ways to draw cards quicker. This is not what the colour needs in cube.
Sanctum Prelate 3/10
While certainly quite a nasty hoser card it is of such low base power that it will be hard to include in most decks. This is a "hate ogre" which sounds as lame as it is. This is absolutely not the new Containment Priest. It is far closer to a Meddling Mage or a Glowrider (bad Vryn Wingamre) than any other type of hoser card. There are some decks this will just end, some combo decks will have fits about this and some control decks might hurt quite a bit. The problem is that it is a 3 mana vanilla 2/2, it isn't getting much work done beyond perhaps preventing some card being cast. It is like a pricey Brain Maggot / Mesmeric Fiend.It is stall rather than full on disruption. It makes building your deck a little more difficult and has far too many associated costs to including it for a card that is only useful in some matchups. Reasonable sideboard potential but still dangerously low powered body and high price tag. I'm pretty sure I would always be playing Thalia Mark One, Thorn of Amethyst, Vryn Wingmare and then like Sphere of Resistance and Gaddok Teeg and so many other cards before I was playing this.
Daretti, Ingenious Iconoclast 7.5/10
Three mana walkers are always an eye opener and this one does not disappoint. This is the best 3 mana walker at protecting themselves, and you for that matter. Churning out 1/1 chumps and gaining loyalty is a potent combination. Having defender on them is a mild drawback and makes Daretti less aggressive but he would absolutely be overpowered if they could attack. They are already artifacts which has a whole world of potential uses, not least of all the second of Daretti's abilities. It is incredibly powerful in an artifact heavy deck where you can flop down Daretti, sac off something spent and kill a significant card of your opponents for just one loyalty. In a deck without many artifacts it will be far fairer, a bit like Dack Fayden when you are playing against artifact decks or not! When you have to pump up Daretti and keep the 1/1 alive to use it next turn to kill something you are being slow and ineffective. Daretti is not a great recovery card. It might be a decent late game stall card but if you are under much pressure and don't have other artifacts then Daretti will not bail the situation. This isn't that much of an issue as he is so cheap. Rarely will you be under that much pressure, if you are then some free 1/1s will sort it right out. As such you will be able to amass some loyalty and some 1/1s and threaten to either kill anything significant they make or perhaps threaten to ultimate. Although you don't need to have artifacts yourself, nor even ones you want to sac, to make Daretti's ultimate work you are then relying on your opponent to have something you can copy. Without the threat of something significant being able to happen with the ulti Daretti is a purely defensive planeswalker. Still a very powerful one in that capacity at least. Again, this makes him similar to Dack Fayden as his ultimate can also be a blank. Both are 3 mana gold planeswalkers that offer insane power level when the situation is appropriate but that can equally be basically dead cards later on.
Weight Advantage - ranging from broken to a mild setback
Narrow but not overly so and abusive with the right support cards. You can pull off the turn one Tireless Tribe win with this quite easily. It is hardly shabby as a 1 mana, 1 card turn two kill combo either... Warping your draft just to pick up dorks with higher toughness than power is likely going to do more damage than good if you pass up the good stuff that has negative synergy with your conspiracy. As such this is probably not a good enough card without the support stuff that abuses it and with such things it is probably a little over powered.
Dragonlair Spider 0
Common, with such a cool name and extravagant cost this should really be a lot better. Even in multiplayer this is pretty narrow and pretty lackluster. Bad bad card.
Spire Phanstasm 2/10
Really cool design and a provider of in draft information which is always nice. Sadly this is just a 4 mana 3/2 flier that might draw you a card. You don't play it in your deck if you wiffed your guess and you might not even if you didn't. It is quite a clumsy card and not insane value at best. I'd much rather me a Muldrifter and that doesn't see much love these days. The fun factor of this card probably makes it cube worthy in the right cubes but powerwise it isn't really there.
Illusory Informant 3/10
This is similar to the Phantasm in what it offers, that being draft info. The card is less powerful but actually more playable. A 2 mana 1/3 flier is fine in the right deck, you can expect to be able to play that without falling behind. A 4 mana 3/2, even with a free card, is just going to get attacked into or Shocked or Force Spiked and leave you wide open way more often than not. So this has a playable body and it offers valuable insight into the draft. This is only useful if you get it early in the draft and so this card is ultimately not worth it. Very cool design and very close to worth it! Situational utility, low power and narrow playability. Shame.
Grenzo, Havoc Raiser 7/10
One of the best cards from the set. Like Edric, Spymaster of Trest but fully ramped in power. Being one colour less and one mana less makes Grenzo highly playable in any aggressive red deck. He is fine on his own, has immediate impact on the board when you have other dorks and he affords lots of options and control. Goad is the weaker of the modes but still very useful. It can force people into unfavourable races, it can force people to chump attack or it can simply clear the path for another round of Grenzo triggers.
The second ability is the more obvious comparison to Edric however it is actually really rather different. You are not really ever drawing cards, you can't hit land, the cards will never be ones you put in your deck, your hand size won't increase and a lot of the time you won't have the mana to play the things you exile. This doesn't overly matter nor stop the effect being very powerful. The exile itself is very frightening for a lot of cube decks, combo control and even some midrange decks really fear the exile of certain cards. While drawing cards from other people's decks will be on average less powerful than doing so from yours it does give you some outs you otherwise don't have access to as the (presumably) red aggro player. Being able to hit a Disenchant or something like that outside of red's colour pie then it might be your best line of play. Lastly, even if it isn't really card draw it should be pretty reasonable value. An unchecked Grenzo will get out of hand very fast.
Skyline Despot 2/10
One of the most powerful monarch cards but really not a card that is going to find a home. You are not casting this, you might cheat it in but it is a little slow to take impact and as such is quite the risk. Obviously if you untap with this still in play and you still as the monarch you really shouldn't be able to lose. That just isn't a thing that is likely to happen. Stick to solid stand alone cards not wishful things like this.
Volatile Chimera 3/10
The ability to have this become one of three 10+ CMC Eldrazi is a thing in cube. That would make this really rather good! The problem is of course consistency. This is not quite as easy to power up nor so smooth in its increase of power while doing so. This is really quite awful until it is a bomb. A lot of the time you won't hit enough super powerful things and this will be a bit of a lottery. I don't much like the design of this one but I can see it being super good in the right kind of cube.
Subterranean Tremors 1/10
Fine enough card with some unusual top end scaling. This is just an Earthquake that doesn't hit players and Earthquake, even the Rolling one, are just that bit too slow to be good in cube. This is a very underwhelming mass removal effect and that is the primary role of the card. Five to blow up all artifacts is pricey and playing this for 9 is almost never happening. The worst thing is that is you were ever acsting this for 9 or more the odds are you would blow up far more of your own artifacts than you would theirs! Cute, perhaps a clever Burning Wish target but other than that not a cube thing.
Regal Behemoth 2/10
Too pricey for the ramp to be that exciting, not a great body for the mana and a little risky being the monarch in green with such poor removal and capacity to block fliers. Powerful card for sure but I don't think it is something for my cube.
Hymn of the Wilds - fun, interesting and powerful in a fair way if a little narrow
For drafting this needs to be seen super early or you won't be able to draft around it enough to be worth. As such it is far too narrow a card for a drafting cube. In a more constructed setting this is one of the better balanced conspiracies, it is powerful but not abusive. Could be a lot of fun to play with this a little bit.
Palace Sentinels - 5/10
Comically I think this is one of the best monarch cards in the set for cube. White is the natural home for the mechanic as white has the best cheap creatures, the best defensive creature mechanics, the best creature removal and a total lack of card draw. Palace Sentinels is just quite a good deal, a 2/4 to defend the monarchy and hopefully an extra card every turn.
Selvala, Heart of the Wilds 6.5/10
I like this one quite a lot and think it is a far better risk for green to take as a card draw tool than any monarch card. There is a bit of a risk to playing Selvala but overall I think even when you do give away free cards you should still wind up ahead. If you make this on curve, which is what you want to do with ramp cards, then you are in the worst position for your opponent to be able to get a free card right away. While this isn't great for you it should be fine because it means they didn't deal with Selvala herself and as such you should be in for a huge influx of mana. It is so dangerous to leave Selvala in play I think it will soon be known that you just kill her, even if you can draw a card. If you don't kill her green will have loads of mana to make an even fatter dork which will in turn give even more mana for increasingly larger dorks. Green is the best suited colour to abuse the momentum you can get from this card and as such she is incredibly powerful.
Borderland Explorer 7.5/10
Not the most powerful card in the set but my money is on it being the most played. This card is the dream! It does everything you want and it does it super well. This is pretty much the best one shot discard outlet on offer. You don't wind up down on cards as you do with all the other cheap ones. You won't find yourself short on mana either. Regardless of your discard synergy this is the best thing to play when you are mana screwed. It is a decent tempo play regardless. It is the complete package for Recurring Nightmare. Even if you are flooded the card is fine as you can thin your deck of a land. I look forward to having access to this card in deck construction. Delicious options! It is even made more interesting by giving your opponent the option as well.
Leovold's Operative 5/10 (draft only)
A draft only card that is basically just another Clockwork Librarian. A very powerful effect in cube where it is possible to have several top picks in a pack late on in a draft. This one is a bit weaker to gain the double pick but it at least a little more playable itself.
Regicide 7/10 (draft only)
This is my favourite of the draft only cards. Not only is it a great removal spell that compliments other black removal effects well and scales better than any of the other one mana options. I like it so much because it gives you free information in the draft as to perhaps what colours to avoid. It might even be worth taking early on just to get that information. Great design and a powerful yet fair effect.
Throne of the High City 4/10
Cute card but so late game I doubt it will ever be worth having to play a colourless land. Decks with lots of mana production and little to no coloured mana requierment might play it but that is about it. In principle the idea of having a land that can turn into a Phyrexian Arena is super powerful but there are some real concerns I have about this. Either you can do it mid to late game because you are so far ahead already and the extra cards won't really be relevant or you can't afford to do it until super late game where presumably you are in a bit of a top deck war. Here the monarch is so incredibly risky, any sort of man land is going to be an issue. I like the card and it is powerful but sensibly play with it makes it too narrow for a maincube slot.
Palace Jailer 6.5/10
This is really quite the swingy card. A 2/2, a Phyrexian Arena and a Swords to Plowshares, the latter two without their usual drawbacks. In an even game this should end it, it has the swing feeling of Sower of Temptation except that it can't all be undone right away with a simple Shock/Terror. While Palace Sentinels is the safer, more rounded and less situational of the white monarch options the Jailer offers so much more power that I can't imagine people not playing it first if given the choice. The best thing about Jailer is that he offsets the risk of losing the monarch better than most other cards. You go a guy up, they go one down meaning they probably need more than just one thing to get out of the situation. Every turn they don't threaten the monarchy they are falling further behind.
Custodi Soulcaller 2/10
Melee makes this pretty weak in heads up cube. It only ever gets back one drops and only ever attacks as a 2/3 while being the target of any old Shock the rest of the time. That basically means this is a Grey Ogre and should be treated as one first and foremost. Even with all of whites great one drops this still isn't playable.
Best normal cards you could add to any cube
1. Daretti, Ingenious Iconoclast
2. Borderland Ranger
3. Grenzo, Havoc Raiser
4. Selvala, Heart of the Wilds
5. Palace Jailer
6. Custodi Lich
7. Kaya, Ghost Assassin
8. Palace Sentinels
9. Recruiter of the Guard
Cards you should add to a draft only cube
1. Arcane Savant
2. Animus of Predation
4. Paliano's Vanguard
5. Leovold's Operative