Just got the marksman diamond badge with a dualgunning marine. It was pretty hard and I got good RNG with TWO jovisec deagles in the rift. I was originally trying this badge by going through mimir for the prototype guns at the nanomanufacture station, but I always found that my damage would fall off at some point. So I ended up rift for the jovisec armor (which I used through the whole game) and the lucky deagles. Probably could have done it with normal jovisec .44s though, since they give more mod spots. Also, build order was extremely important.
It was sog, sog, gunslinger (at this point you can start reliably gibbing early level enemies), army surplus, army surplus (if not, I would basically always run out of .44 ammo), gunslinger, gunslinger (super important to get rid of the extra fire time when reavers are around), wizkid, wizkid (second rank for extra crit damage and crit chance on the armor), sog (goal was to get to 200% crit chance, which I think I almost did with an av3 pistol amp that gave +40% crit chance), then hellrunner/whatever.
I also sacrificed the frozen heart for +50% damage, though there were times after that when I was a little worried about health. Oh yeah, AND I got the ancient legwrap for +20% movespeed with no penalty. Crazy lucky run.
In general, I'm finding the masterless diamond badges to be the hardest ones. This is unlike DoomRL, where going masterless could be stronger in some cases than going for a master. The master traits in Jupiter Hell are just too good.
Anyway, now I have 12 diamond badges, and only need three more for the god hand rank (which I think is the final rank?). I can definitely get the CRI diamond at some point, and have been trying for shottyman (though that's pretty hard tbh). Berserker also seems doable, probably that and CRI next. NY reload seems insane, but I guess a wizard build could do it (but I hate the wizard playstyle). And gauntlet seems annoying (endless diamond was easy af though).