This cube is designed to be as non-parasitic as possible. Most cards have a relevant race/class. The archetypes are as follows:
WU - Party
WB - Clerics
WR - Warriors with equipment subtheme
WG - Warriors with go-wide subtheme
UB - Rogues
UR - Wizards
UG - Ramp (this is the least-defined archetype and is basically another flavor of elves)
BR - Vampires
BG - Elves
RG - Goblins

When drafting this, we use a modified "Minneapolis Draft" (credit to Ryan Overturf) where instead of eight boosters, each person opens ten boosters. We found eight is insufficient to generate a critical mass of tribal cards. It's possible nine would be ideal--we haven't yet tested it.