Lightning bolt was too strong, so replaced by shock.

Splinterfright doesnt mesh too well with the other golgari cards, and scurry oak would fit nicely in both the simic and selesnya color combinations

Cube version 4:

: Boros was too swingy, and also quite strong. In this update, the power level is toned down a bit, but the consistency of the deck should have improved.

Heavenly Blademaster and Maul of the Skyclaves were the biggest problem cards, and have both been removed. Fighter Class was added as an extra option to search for an equipment, making it slightly more consistent.

: Izzet was decent in power level, but had some cards that strongly suggested an aggressive approach, while the majority of cards were controllish. These cards have been replaced for more control-oriented cards.
Sprite Dragon to Expressive Iteration is the biggest change. Also, the weakest cards in blue have been removed and have been replaced with generally good spells.

: Golgari was the weakest color combination in the cube. The power level of the cards was decent (although slightly weaker than the rest of the colors), but the main problem was that it felt inconsistent, with high probabilities of milling the cards you needed to take advantage of the full graveyard. To combat this, more cards have been added that have an effect when they are in the graveyard, in stead of cards that use the graveyard outside of it. Some small defensive creatures were also added, to be able to stave off the aggro decks of the format better.

Overall:

Some small other changes were made:
Lurrus of the Dream-Den saw play outside of Orzhov more often than inside it, due to its hybrid mana cost. This is not the idea of the golden cards, since they are bonuses for committing to a color combination. So it was replaced with Drana's Emissary.

Ulamog's Crusher and Thran Dynamo were too weak for the cube, and didn't fill the role they were supposed to, so they were replaced with the better Myr Battlesphere and The Celestus.

Some other general cards were also changed, because I felt like it and I like to keep the cube fresh.