A mixed aura, who would've thought? I guess that explains why they pull pranks and annoy people. True monsters cause destruction. The Boys, on the other hand, only pull mostly-harmless pranks. I'm guessing the white part at least keeps them from causing a ton of destruction while the black part causes them to pull those annoying pranks.
So they're both good and bad. So basically the fact that they're boys(let's face it, boys aren't always very good), and that their "upbringing" wasn't good made them bad and the good part of them was hidden. O_O X) Now they just hafta succumb to the light and everything will be a-ok. XD