Some cards, such as the aforementioned Mental Misstep, are excluded for either power or diversity reasons as I don't want any card to be objectively better than its counterparts (Lightning Bolt is excluded because of this rule for example);
Color balance and a 50%ish ratio of creature was kept for the first iteration to stay close to a normal cube experience.
Archetypes:
+1/+1 counters (W/G/b)
Heroic/go tall (all colors)
Go wide (W/r/g)
Mill (U)
Kicker/big mana costs (every kind of alternative cost which allows you to cheat the power of the cube) (U/G/r)
lantern(ish) control (U/r + colorless)
Sacrifice (B/R)
Goblins (B/R)
Zombies (B)
Elves (G)
Saboteur/unblockable (U/G)
Prowess (R/W)
There are some build around cards highlighted in the list.
Let me know if you could test the cube and what you think about it, any feedback is appreciated.