I've always wondered about this, regarding the elements

I love when people ask about the darkness element. Shammos uses dark magic, he's chained up. When Grendel tried to use dark magic, he created the zombie lupins. Faust was created as a result of dark magic. Dark magic, at least in MS, creates evil things.

This will hopefully be clearer when Monster Book is out, I recall Hobi from Leafre befalling a similar fate to Shammos. That's basically it though, there's a reason, however flimsy you may consider it, as to why there is no dark element in maple, and that's because it leads to inevitable corruption into a goblin type thing. It works for Nightwalkers because they're only drawing on the power of the sprite.

That being said, depending on how they work the Black Magician disciple group (If it does get made) then you might see it. At this point in the game I don't see new elements being introduced, especially dark.