The Fall of Thraben is an unpowered themed cube that builds of the themes, ideas, and flavor of Shadows Over Innistrad and Edritch Moon. Each color pair has its own sub-theme, but there are four overarching themes in this Cube:

Death: Cards that care about dying, other creatures dying, or sacrificing creatures.

Rebirth: Cards that bring themselves or another card back from the Graveyard, or Spells you can cast from your Graveyard.

Graveyard Matters: Cards that utilize the Graveyard as a resource and the cards that stock the Graveyard to power these cards.

Tribal: Cards that care about one of the five main Innistrad Tribes: Humans, Spirits, Vampires, Werewolves, or Zombies.

Additionally, there are five 'Partner' cards that, when drafted, come with one or more
extra cards:
Giselda, the Broken Blade comes with Bruna, the Fading Light.
Docent of Perfection comes with Aberrant Researcher and Delver of Secrets.
Cauldron Familiar comes with Witch's Oven.
Hanweir Garrison comes with Hanweir Battlements.
Arachnus Spinner comes with two copies of Arachnus Web.

Credit for the Partner Cards idea goes to CavsFangelo and his amazing Cube of
Cthulhu! http://www.cubetutor.com/cubeblog/115848