After the newest playtest I got a chance to gather some insight from my players, this update is mostly the result of those conversations.

Firebolt and Reckless Rage have been waiting in the sidelines as interesting burn spells for which I have no space.
I had no space, until I cut Ghitu Slinger and Rift Bolt.
Ghitu Slinger is a lot of mana for the full value and doesn't play well with Young Pyromancer and other spellslinger cards.
Rift Bolt always plays a bit worse than it looks, it's a good rate of mana to damage but the problem is the timing.

Confounding Riddle is a clear upgrade for Supreme Will, I'm not particularly hyped for this style of power creep (Deep-Cavern Bat is another example that I'm choosing not to include). Supreme Will was at a fine power level for my cube and I don't want to be constantly upgrading cards that are doing ok and that my players are already familiar with.
On the other hand I'd like to get a bit more self mill in the cube and I love the art for Confounding Riddle so it gets a pass.

Wizard's Rockets are pretty useful for splashing and are easy to include in different styles of deck.
Batterbone has been played very little and to equip has proven to be too much mana.

Ulvenwald Mysteries seemed good value but it never panned out. Green decks are rarely using it to its full potential by sacrificing nontoken creatures, instead it usually stays in the sideboard leaving space for more threats and ramp.
Oviya Pashiri, Sage Lifecrafter has a similar effect to Imperious Perfect and that's a really promising comparison as the Perfect is one of the better green cards in the cube.

Aether Adept is a victim of the "too many Man-o'-Wars problem", between Vapor Snag, Riftwing Cloudskate, Callous Dismissal, Into the Roil, Man-o'-War, Mist Raven, Wash Out and Repulse there are plenty of other bounce effects in the cube.
Frost Trickster is worth testing as a flying Frost Lynx, and it should fare better against creatures with ETBs than another bounce creature.

I really like explore as a mechanic, Spyglass Siren is the one inclusion I'm willing to try out because it fits the cube a bit better than Cenote Scout, River Herald Scout or Kinjalli's Dawnrunner.
For some reason I was stuck trying to keep a 2/1 flyer at , but I expect that a costed flying creature will play better with ninjas and in the flyers archetype.

Cartographer's Hawk is an interesting intersection of aggressive strategies and midrange value. I'll keep an eye on white weenies to see whether I've cut too many cheap creatures like Skymarcher Aspirant.

White has a problem with mana value 3, Ossification over Prison Sentence lessens the bottle neck effect without being an obvious first pick (and notably it is worse in 4-color goodstuff decks that may get stuck without basic lands in some hands).

Goblin Assault has never been better in the cube given how many sacrifice outlets there are in red. Unfortunately its best is still underwhelming.
Imodane's Recruiter has proven itself surprisingly strong in WOE limited and I'd like to give the card a chance in the cube setting.

Phyrexian Rager is simple and effective but it isn't a necessary piece for any strategy so it's not high priority.
Over the Rager I'd like to try Gorex the Tombshell, it offers more value and pushes players in a clearer direction.