From the release:
One of the most flexible aspects of games of Fanticide is the ability to create new Warbands. We have always wanted this to be a game where player creativity can come to the forefront! We also want to create new and exciting rules and warbands to explore the world of Nowhere here at the Dungeon and have decided to bring you the Blood Tree Warband!
This is not simply just a new warband though-it is a great new way to play a game with the new Soul Thrall rule. Everything in the warband must stay within a certain distance of the Blood Tree or they lose their power to activate. Think of all the great games you could play using a variation of this rule - perhaps a magical idol has animated a group of golems, or a powerful Lich is controlling a band of Undead. This rule has been specifically created for war bands led by magically powerful legends or creatures capable of controlling the minds of others.
A Blood Tree Warband consists of the Blood Tree and various Flora he has corrupted with his malign influence. Drained Forest Fathers and Drained Tree Bogies reanimate under his power to bring the Tree more souls. Gore Cap Mushrooms sprout up in the Mourning Woods created by the Blood Tree's hunger, infecting all who get close.