What are yours? And how would you model them as a PC faction in DW?
I came across an idea, did some research and blatantly stole a lot ideas to make one up, mostly as an exercise. In all probability it will serve as antagonists but I am using Rites of Battle & Honor Thy Chapter to 'design' them. So seeing other Chapters that are considered odd might help.
A final note before I let everyone let loose their creations; by definition all Space Marine Chapter are special snowflakes. Not necessarily to the most extreme degree but they almost always have something that makes them worthy of awe & respect of other Astartes. So please try to refrain from flaming these Chapters.
They are meant to be that way, just let it go. It's not like they are cannon anyway.