i think i can understand the unversed on why they are based on negative emotions or at least vanitas's remnant at best for the unversed are people's negative emotions right? so you could say vanitas who altered other people's negative emotions and turn them into the unversed we know turned his own negative emotions into vanita's remnant and because their's "remnant" in vanitas's remnant's name you could also say that the unversed are also remnants of people only before vanitas.

They're literally extensions of himself. I don't think he can just turn people into himself (unless, you mean just taking their emotions, person still left behind to regrow new emotions later). I think messing with people's emotions is a good way to get the Heartless stirred up, though. As a precursor to the later events, I think the damage Vanitas did set up the worlds to be easy targets. I don't think he actually killed anyone, just weakened their hearts.

 

Interestingly, being an emotion eater isn't a new thing. It has its own trope page: http://tvtropes.org/pmwiki/pmwiki.php/Main/EmotionEater

 

Lastly, the remnant thing is just a common thing with this series and not necessarily tied into 'canon' - Terra's armor, in KH2FM is a remnant (per the Japanese using the word 'sentiment' instead of 'remnant' in both Terra's case and in Vanitas'). The absent silhouettes of Organization XIII in KH2FM, the early members, are also remnants, although instead of using armor to hold their identities, I'm pretty sure its contained within their weapons. There's no real rhyme or reason for them to be there other than to spice the game, and their existence may not be 'canon'.

The entire Unversed creation confuses me actually

 

~Shrugs~