Highly overpowered! Extremely balanced! Synergistic! Not a colour-pie-break in sight! Compelling tribal mechanics (?)! It's all here!

Colour themes:
White: Cleric/Elephant/Dragon tribal, mass land destruction, land reanimation, auras/enchantments, random hosing of other strategies
Black: Thrull/Nightstalker/Saproling tribal, creature sacrifice, swamp sacrifice, reanimation
Blue - Leviathan/Serpent/Cephalid/Homarid tribal, island sacrifice, islandwalk, tap effects, creature sacrifice
Red: Lizard/Salamander/Dragon tribal, land destruction, land sacrifice, storm, general chaos
Green - Beast/Saproling/Wurm/Squirrel tribal, land sacrifice, card draw, self-mill
Colourless: ramp, land reanimation (phew!)
Multicoloured: Atog/Avatar tribal, Cascade, mana cheating

Optional errata:
Jolrael, Empress of Beasts: the lands also gain the creature type Beast and are named Carnivore until end of turn. What sort of empress would she be otherwise?
Dandân: creature type changed to Leviathan, 'cos look at it, it's huge and this ain't Segovia!
Thrull Retainer: now a Tribal Enchantment - Thrull Aura
Worm Harvest: Worms are also Wurms. Sorry, I don't make the rules.
Realm Razer: Phases out all lands instead of exiling them, using Oubliette's wording. Wouldn't want to lose all those enchantments so easily!

Extremely optional errata:
Riptide Mangler: Added creature type Serpent
Saprazzan Breaker: Added creature type Leviathan

I can't quite promise that land sacrifice isn't one of the main themes of this cube...

Have fun!