The layout in this book is off the chain, and the character art is amazing. Your PCs are mechanically distinct and have a lot of personality, and you've come up with a lot of neat hacks of the basic Havoc Engine rules for their abilities. I like the idea of the mutations, but I'd like to see combination of positive and negative in them. I also see the mutations stacking up pretty quick and downing characters; I might suggest separating mutations from conditions inflicted by adversaries or as suggested, make mutations a bit less likely to actually occur. Separating stress from conditions is an interesting choice, and I like the Overdrive ability being a pure positive to give that burst of power as things heat up. Your adversary and location descriptions give the perfect combination of funny and horrible; I do worry that the number of powerful adversaries at some locations could be overwhelming. It would be nice for the companions to be foregrounded more mechanically to emphasize the connection between pet and owner. Overall, a really solid entry with a lot of room for growth.