Was at 1 extra card, so I'm removing Narset since her power is un-fun and not even as good in cube as constructed. Puts me oddly low with planeswalkers in blue, so I may come back to that and add 1-2 but we'll see.
Unfortunately, I'm removing most of what I literally just added. As much as I like the cards, the ones I had are better suited for my environment so I shouldn't remove them without large-scale revamp. Cutting Braids is painful, but the aristocrats theme is better without her honestly. Rankle just does the job better.
Removing Anafenza because the WW cost is too prohibitive, even in the GW persist-combo deck. It can still come together with cards that are decent outside of that deck.
Archmage's charm out since UUU is hard enough and I had to cut something. Aspirant back out as well, but it'll be there when/if I go hard into +1/+1 counters. Red was at 59 cards and needed a 2-drop so I went with Kargan Intimidator since so many people were recommending it.
Blade Splicer doesn't quite hold its weight enough anymore with me adding in Taranika. I like the card, but I don't have a flicker theme despite having a few cards that do have that effect. Basri's Lieutenant is cool and would be great when I finally decide to pursue +1/+1 counters further, but I'm keeping Mothra for persist combo since Fiend Hunter, Birthing Pod, Recruiter, Vannifar all help me find pieces and Anafenza, Mothra, and Heliod all go infinite with Kitchen Finks, first 2 also with Redcap.
Giant Killer is just more interesting than Isamaru. I want more decision points and flexibility in my games. White doesn't win pure aggro; it needs taxing effects too. Harmonious Archon was an oversight earlier so I'm adding it by removing Sun Titan, and I miss Hero of Bladehold.
It felt like it had been a while since I last updated. Turns out I updated with M21 and just haven't revisited after spoiler season or for any of Zendikar Rising, so not a ton to add. A few are more trial and not obvious inclusions but I figured were worth the shot. The introduction of MDFCs is incredibly interesting for cube design, and it makes me wonder just how far I can go down the modal route to ensure the best play patterns in my cube. I'm not going too hard into it yet, but with the next 2 sets having more, I may look to push that going forward.
More specific notes:
Red seems to be in a weird spot. I have a few too many 4 drops, maybe need to remove Ilharg also, and I feel lacking in the burn spell department.
I also have a clear tendency to go towards graveyard-matters cards and have a lot of mill, especially self-mill, in UB that I'm not certain is super well supported from an archetype standpoint. Reanimator is absolutely a deck archetype I want to include, I'm just not sure if incidental milling is the way to go with stuff like Mire Triton, Sinister Sabotage, etc. TBD after some playtesting.