After forcing UR a few times vs bots just to build some decks...

• Casting multiple spells seems both fun and easier to build around. Get in, Jori En.
• The deck really wants more cheap draw spells to balance the glut at 3... but cheap cantrips also conflict with the role cycling is generally playing.
• There's tension between wanting to include the "Banishing Knack" combo with several artifacts, and having enough instants & sorceries for those specific payoffs. This puts more importance on "noncreature" and "2nd spell" cards and a desire to reduce "Instant/Sorcery"-specific payoffs.
• There's also a tension between what the deck needs for the theme to function, and cards that are just "too good" to pass (Goldspan, Alandra, Mystic); I'm hoping this is just a bot phenomenon.
• Relatedly, I can look for more overlap with U artifact payoffs that would play well here.
• On the plus side, it adds more dynamics to existing cards like Cloud of Faeries, Esperzoa, Squee, Goldspan (did it need it?), Aetherflux Reservoir...
• Reverberating Summons fits OK mechanically but I'm not convinced that it's worth the wordcount & complexity for what's basically a role player. It does "sacrifice" and rummage, but I think that's an overlap trap (an overtrap?).

And after all that, only a few actual changes...

• Scarab & Djinn both seem potentially too strong, but Djinn is simple yet exciting, and Zombies needed a bigger payoff in blue (especially since Advance would've gotten even worse now).
• I love Ghostly Flicker, but I want fewer 3s and the double-blink matters less than having any blink, so I'm reducing the cost and adding a +1/+1 counter.
• I initially rejected Proft's when it came out because it's a wall of text and a little confusing. It still is, so that's a risk, but it's also a perfect UG card that slots well into this new UR iteration. Worth trying.
• Likewise, Synthesizer is also a risk. Like the Summons it's replacing, it's not a new-player friendly card, but it is a cleaner "sacrifice" plant, often casts 2 spells, and satisfies the "cheap cantrip" and "artifact" notes above. (I'm excited to see it next to Esperzoa)
• I considered Alania's Pathmaker over Harnesser, but I'd rather the red "exile" effects read the same throughout ("this turn" vs "next turn"), and Harnesser is better Jori/Kraum redundancy to keep chaining. Barbarian keeps getting cut from my decks, and there's enough artifact removal anyway.

A 3rd update in <2 weeks? And 6th in 4 months?? What is this???

UR has still felt dissatisfying: it's the classic A-B conundrum, wanting to play payoffs early (turns 2/3) then play spells after... and falls flat in any other sequence. Fittingly, new Tarkir offers that what's fun about this strategy is the flurry of casting a bunch of spells, not necessarily JUST instants and sorceries. I'm starting with a significant but limited change for testing purposes, but willing to revert some back (like poor Balmor and Infantry!). The Strix has also always been more of a filler/signal than an exciting card, so that might stay off. If I like how Kraum plays I'll consider Jori En, but Wandering Mind seemed better for the consistency issue. (I also considered Impulse and Reckless Detective, but ultimately passed)

Other changes:
Enduring Innocence fit exactly how I wanted - fun and strong but not busted, fit several decks' themes - but it also broke the rule of needing to LOOK like a bomb: its only 3 mana, confusing, and understatted. Drawing cards is fun, but it wasn't clear to folks just how strong it was (whereas Tenacity's fit/power is much clearer). I'm trying out Bond, but I'm open to other ~5-mana "finishers" that fit most of the white archetypes. (Considered Militant Angel, but that was also confusingly worded).
Carrot Cake was indeed way too wordy, and folks missed that they'd get another 1/1 when it was sacrificed. Trying Cat Collector, which seems not only more straightforward, but a better engine payoff for BW (a good Witch's Cauldron or Spark Reaper combo).

With another decently big +1/+1 counter creature just added (Dragonborn), I wanted some other minor payoff for the counters: Duckshell Crawler seems perfect. And having cut Faerie Vandal, blue feels like it doesn't add much to the archetype besides Amass - which black has more of - so I'm trying out the Skymage. It's possible it should be Thopter Mechanic, or swap back Mystic for Vandal (Mystic played well last draft), but Skymage seems like a decent engine piece and high-risk-high-reward play.
Academy Elite has felt narrow, wordy, kinda weak, and also misleading for anyone looking for +1/+1 counters.

Boston Cube Party was awesome!
It was also a good reminder that while combos & engines are fun, spinning your wheels endlessly is not: games need to end. As I make updates, I will continue to keep that in mind.
To that end, Loaming Shaman's time is past due. It's a trap for newbies (mostly with the intent of getting good cards back into their deck to maybe draw again), and too easily removes the risk of milling out from Slide/Protocol decks. I continue to be satisfied with the amount of answers to gy shenanigans (mostly by exiling loops when they're on the battlefield), so its utility as an answer also isn't high.
Decree of Pain is another card that's been in the cube FOREVER, but I so rarely see it played, it doesn't fit "cycling" things that well, and is made a bit redundant by the new Archfiend.

Having only 4 reanimator spells has felt a little light after cutting Whisper. I'm trying out Revoke Demise since it seems OK in BW lifegain as well (getting back a key creature AND gaining life immediately); we'll see. And imagine my surprise when - as I was browsing Dragons in case I could make Teeming Dragonstorm work - I stumbled across Ambitious Dragonborn! What a perfect little green "Zombify" that works in basically any of the green decks, but at its best when you can consistently cycle a large creature (like in a GB shell).
Frontline Rush seems perfect, and I can't remember the last time I saw Hedge-Mage played. Appraiser seems more like what I wanted than Organ Hoarder, so trying that instead of the awkward Fear.

Goodbye hexproof: I already got rid of Plating, and now Veil is going as well. Although it's ostensibly important to protect big creatures, it's also a lot more fun to create a back and forth (and is frustrating when someone counters your big removal spell). White still has Valorous Stance, so it's not completely without protection.

The Enchantments deck is really fun when it's drawing tons of cards, so I relented and added another Enchantress (despite a new 1-of ability word). I risk adding too many parasitic cards only good in WG, but it's a deck that a couple people players really enjoy so I'm not super worried. Eidolon might also be OK in GU or something as well.

Still waiting on Tarkir previews to see if anything there fits.

One more thing: I've yet to see anyone use Lazotep Plating correctly for its Hexproof purposes. I think it's just got too much written on the card, so I'm exchanging it. I do probably need another Hexproof spell (You See A Guard Approach; Dive Down; etc), but an exchange spell is a bit flashy and seems fun so I want to try Trade first.

I'm happy with a few additions from Aetherdrift: Black has been looking for another good reanimation target outside of green (I love Whisper... but it hasn't been in a deck in forever); I'm excited for Magmakin to reintroduce a 3-card infinite combo; Wreck Remover is a perfect little role player; Rhet-Tomb Mystic is perfect as a 2/1 flying zombie wizard... that sometimes helps a cycling deck (less than it looks like on the surface).
Where I'm less clear is Marauding Mako (Hopefully more flexible than the 1/2 menace that demanding exactly cycling?), Aetherjacket (I never lived the Broom dream sadly), and Scrap Compactor (strict upgrade... but a lot wordier, which I don't like).

I also moved all the Landscapes and the newer 3-color cards to the Maybeboard. I haven't added them to the physical cube yet, and online it's disrupting tests; maybe I'll just swap in other 3-color cards occasionally.

Little here is certain.
Where Faerie was cooler but hard to answer, Mystic might be "easier" to answer, but overall stronger. Will depend a lot on player reactions, but I might switch this back.
Elas has seemed a bit too strong, but also isn't a payoff for lifegain as much as an engine, so I'm trading it while maintaining a drainer with the new Bloodwitch. The lion has been pretty complicated and also underwhelming, so trying out the clean anthem. Blight-Priest likewise hasn't seemed great, so trying out Tenacity (but might be too strong/annoying).
I've never been happy with Skola, so trying out Squirrel to see if it feels cooler.
Lastly, I wanted one more flashback card. Nibilis has always been decent if unexciting, hence its survival; I'll see if it ever comes back.

A mostly mouse-sized upgrade of a bunch of cards, with a couple main characters finally getting killed off.
I love the dream of Nucklavee, but no one else picks it, and it often leads to frustrating loops; Angler is just more in line with what the other UR payoffs are. (It also means I feel better bringing Cackling Counterpart back). I added a couple more untap effects (but removed Mirran Spy) to make the Knack/Helix thing a real UR payoff... we'll see how that goes.
Roar of the Wurm is great in theory, but a 4 mana 6/6 is not really worth the work to get it in the gy nowadays, and not being a creature hurts its place in other BG styles (like Spider Spawning). Testing out Thickest, though that might be too swingy.
I'm also swapping out the LOTR cyclers (except for blue) since they felt a bit too strong. They're borderline, so could make a return some day. For now, testing without them.
A couple notes among the minor upgrades/side-grades: I'm testing scry on Carrot Cake (it's still LESS complicated to read than Haunch); Instant speed removal is important, but feels bad at efficient rates, so I'm trying to shift to avoid cheap, unconditional surprises (e.g. Exorcise; Seal of Doom; Agate Assault) since at least when someone leaves 4-5 mana open and still has cards in hand, that's suspicious enough that you might avoid making a cool play that could get blown out.

Although most of the MH3 themes don't fit this cube, I'm still excited about some of the black cards we got. Mindless Conscription in particular might honestly be too strong, but we'll include it for now. And I'm shocked to be saying goodbye to Reassembling Skeleton.
Speaking of too strong & cutting a mainstay, I've finally come to terms with Deep Analysis: It is not fitting my objective that powerful cards look the part, and it has saved me from so many losing games (or put me way over the top) even though the other players think they really lost to Deeproot Champion or whatever. There's enough card draw in blue that I'm trying another tap effect that can still draw a card.
As for what's leaving: Dire Moon just slows the game down a lot: vs a big & small threat it can't attack, but that also means the opponent also keeps their big threat back to block, creating big stalls. Hopefully Larva being 5 mana and bigger will help this phenomenon despite creating another small deathtoucher.

Lastly, I'm excited by the landscapes but I'm not sure how to get land counts appropriate, so I'm just going to experiment and add 15 new cards (1 pack): all 10 landscapes and the 5 3-color combinations I don't have. The latter especially presents some risk since those tend to wheel a lot more, but they can also be exciting so we'll see what sticks.

After sitting on this a while, the Varmint is the only card I'm adding. Strong consideration for Reach for the Sky, but will need to ponder a bit more about its replacement.

I almost forgot about this swap. Creating an army of 4/4 Nucklavees with Counterpart is fun for exactly one person exactly once. Counterpart is also secretly one of the best blue cards, but doesn't read like it, so I'm cutting it for that reason as well.

Boards still get pretty cluttered, and my playgroup seems to enjoy green, so I'm adding a couple more removal spells to make sure everyone gets their fill. (Also, Sailback just sat in folks' hand until they saw an artifact/enchantment, which feels bad when they don't). Panther gets in because "it's cute!" and I can't decide if the reach on Ancient has been necessary or backbreaking.
I opened a Melek, so testing it out instead of the other newcomer (seems more exciting for someone to play)
I'm also testing the enemy bicycle lands (again) to see how it plays out instead of just hoping they print them someday. The current suite of enemy lands is just pretty unbalanced in terms of power, and I'm honestly OK slowing down RW.

I thought the Thriving lands would be a great, newbie friendly solution to manabases: if you're one of those colors, take it and play it. Instead, they've been a little confusing and involve memory issues, so they've mostly benefited my off-the wall 4-5 color decks that don't need help with the addition of LOTR landcyclers (1-mana has been HUGE for speed). Until I figure out something better, these are switching back to a variety of artifacts (including perfect newcomer Runaway Boulder!)
Seismic Monstrosaur is perfect. The other landcyclers were decent but not enough to replace what I have.
Beanstalk I'm unsure about; might not work well, but testing it out. Could be Cease//Desist? (which is kinda green, right?)
Planar Cleansing hasn't been exciting and doesn't fit the W decks, so testing out a more straightforward removal spell.
I'm also writing "Zombie" on Virus Beetle, haha.

Lastly, at our most recent draft I randomly had in Pierce Strider as an early Thriving land replacement... and someone combo'd out their opponent with that and Escape Protocol, so I'm officially leaving it in (for now).

Somehow "Remove/Replace" didn't get clicked.

In an effort to reduce hard to answer "win the game" cards, Oran-Rief Ooze is just too strong. Enough of the "+1/+1 counters matter" cards are self-contained and UG draws enough cards that I don't think the theme needs more help. I'm also excited to push UG more towards "heroic" (without the keyword) since it melds well with GW and helps give purpose to other cards I want in the cube, like Banishing Knack.
What does need help is UR, which is getting 4 new cards. I just realized it's the only color pair still with both hybrid cards, so it's getting an upgrade that doesn't need to be played before all your spells. I'm also trying Song and Alchemist - both of which could be too strong - instead of 2 cycling payoffs: Adept (which everyone kept playing without being super aggressive or having any ways to discard) and Stinger (I lose a Wizard, but had little purpose otherwise). Relentless Advance was too weak before and might still be, but it's simple and enough of a mild role player in a few decks that I think it's worth trying again.

The Drake Haven switch has been good (so far), so I need enchantment removal much less. Other options for this slot besides the Bloodline were Up the Beanstalk, Invigorating Surge, and (from a previous post) still Mother Bear, Garruk's Companion, and Dreampod Druid.

Lastly, I can still make 4-color decks with ease, so the mana might be too good... but folks also might not be taking lands highly enough. I'll be considering cutting the Thriving lands in the next update until that trend changes.

I decided Collector's Vault was worth trying as yet another mana fixing, card drawing artifact (so hopefully ok in RB, UG, ramp, etc.) that's yet another Ocalchase Daredevil combo. Scrabbling Claws is a nice gy answer, but gy strategies haven't felt oppressive and there are other answers, so claws only looks good alongside Furnace Celebration or something.

I finally got to see Spiteful Prankster in action, and it was super obnoxious for all of my opponents - Definitely MVP - so I'm downgrading back to Iguanar, which will hopefully be easier to deal with (and not as potent in combat). It turns out boards get pretty messy when everyone's trying to setup their engines, so abilities like that on Iguanar and Falkenrath Noble are very hard to overcome and even see coming (just the sudden realization that combat will result in your death); "you control" will be a good line of text to look out for to replace these with as well.
Likewise, Stone Haven Pilgrim can feel oppressively strong when it's turned on early since it's both a 3/3 for 2 and turns off the ability for the opponent to race. Opting for the simpler 2/2 Lifelink.
Lastly, only a couple of Eldraine inclusions, sadly (especially for an enchantment themed set!): Flick a Coin is exactly what I would've wanted when I added Improvised Weaponry; Sprite is an experiment, and even though I just added Recon, it's not always obvious to people when to put that card in their deck, so it's still the most flexible Blue slot.

At the risk of angering purists who think other IPs don't belong in Magic, I'm adding the new Landcyclers and a couple of other decent cards. Seems fitting that green gets 3 landcyclers. Legolas seems possibly too strong, but worth a shot (I also can't remember the last time Commune made it into either GW or GB). Rosie seems really cool, since tokens are everywhere (>1/6 of the cube makes a token) and will be fun to discover different places she fits. With the previous addition of Elas, 3 static death->drain effects are a lot, so I'm subbing Cutthroat with Return to Action (definitely weaker, but still lifegain related and can lead to some fun moments).
Lastly, Visionary is great but barely fits one the GU theme (plus green is becoming really strong already). There's been an appetite for griefing other players, so I'm trying out Kavu over options like Mother Bear, Garruk's Companion, and Dreampod Druid.
RIP Eternal Dragon.

I didn't realize Alandra existed, so testing out the swap with Drake Haven. Pros/cons to both. Might switch them back; we'll see.