Firstly thank you on behalf of Chris Templin (Cianty), myself and everyone who contributed their time & valuable ideas to making the BTB experience happen in a big way for Mordheim lovers.
Corrupted Characters offers some new options & pointers to help direct some fantastic material which already existed and just tended to get overlooked in the heat of battle during campaign play.
I think that the information you're looking for is included on page 1 of the document. The first page was intended to outline when/where mutations just 'happen' in order to promote scenarios set in the Northern Wastes territory which you will find in the BTB supplement. The same applies in new scenarios you might design for yourself! Plus
in any traditional scenarios or favourite custom scenarios (Harpy Hunting anyone!?) which you choose to play if you agree the games can take place in the Wastes during your group campaign, instead of where they would normally occur. Go for it!
You can ignore the hiring rules for mutants in the Cult of Possessed warband rules, as Corrupted Characters is geared to describe the ways in which warriors become mutated during the course of
All warbands which we shall classify as 'followers of Chaos' (for simplicity in a forthcoming release) have the option of taking the mutation, or gift if the Hero has a Mark of Chaos
. This means if you don't have the gold available to pay for the mutation you can't benefit from it. Think of this as a tithe to appease your hungry patron.
Warriors from warbands not loyal to Chaos are sometimes struck by mutation. This is not a choice! The mutation applied is randomly determined and there is no tithe to pay.
Ok I hope that's not too boring.