You remember how there were two of you? Kind of the same thing, only Dark Aura copies are basically limbs more than actual thinking things-and they can copy anything, not just you. Even inanimate objects, like swords, which is why I keep making that limb comparison. You can only have 10 of yourself in terms of Dark Aura copies, counting the original, but that's about it for a limit...

I mean, you don't have to if you don't want to. BUt I advise doing so.