That's a pretty tricky one to answer since I'm not exactly good at making bad guys. Imagining my own characters in those positions is pretty difficult. But I can give it a shot!

Asheron: The bunny could be an all around trickster that you'd find in the forest. With his ability to jump around from plant to plant at will, he could easily frighten people enough that they get desperately lost. At which point, he'd be able to pounce on them for an easy meal~

Trey: I think he'd end up just following in his father's footsteps and become a big name bounty himself. With his need to fight and already having no problem with using underhanded tactics to win, all he needs is to throw away his honor and he'd be right there!

Reath: I'd say his disinterest in boastful people would just send him into using his powers to put them down and keep them down. Since people needlessly putting themselves or others in danger is his biggest irritant, he could also go out of his way to get those up and coming rookies blacklisted from ever being explorers.

Kimoru/Mukiro: N/A (They're very much me after all. Thinking about them being evil wouldn't be good for my head XD)