So I wanted to create a cube that really allows multicolor strategies to flourish. But I didn't want to limit the synergies and strategies to only certain cube colors, so I looked to the Guilds of Ravnica for guidance.

I first added the guild keyrunes, the guild mages and the gold mages. I then picked one of the available guild leaders for each guild, I also added the guild charms, and then settled my multicolor section.

In terms of lands, I added the Karoos, the LifeGain lands, and the Scrylands for color fixing and utility. One of the reasons I chose keyrunes over signets or anything else, is that keyrunes also have an impact later in the game by becoming a creature. This was about all the lands that I wanted, and I was debating about the guildgates for a while. However, I didn't really want a gate subtheme, and I felt that evolving wilds was just a better color fixing option. So that settled the mana/color fixing section.

Now the goal is to find all the monocolor cards I need to support the strategies of the guilds - ideally one card can support multiple strategies. The list of the strategies I want to support:

Azorius: UW Control
Boros: Aggro/midrange Flyers
Dimir: Control/Mill/Disruption
Golgari: Control & +1/+1 Counters (Sacrifice Sub-theme?)
Gruul: Aggro/Midrange +1/+1 Counters Beatdown
Izzet: Spells Matter / Beatdown (Copies Subtheme?)
Orzhov: Control (Life Matters Subtheme?)
Rakdos: Aggro Beatdown
Selesnya: Token Beatdown
Simic: Midrange +1/+1 counters Beatdown