Applying the ideas of elemental manipulation from Avatar: The Last Airbender and trying to drop it in a medieval/Renaissance Arabian setting has given me some ideas regarding how I would have it interact with the world.
I was searching for ways that the elementality of the djinn could follow through into other areas of their life, or might spring up around them involuntarily. The original idea was for the sword of an Ifrit to either set ablaze when he was angry, or else singe and burn at the best of times, and having the Eloi's blows land with small thunderclaps. But I was having a hard time with subtle offensives for the Dao and Marid. So far the best I've come up with is the Dao's blows simply having the weight of stone behind them, and the Marid to flow around a fight and dodge easily.
Having them have access to the signature water whip or stone armour/gauntlets occasionally seen in the cartoon series was already a given.
Other ideas that I've currently got involve the current djinn as being the descendants of humans and true djinn, hence their lesser abilities and more human appearance. I think the corrupted djinn may be the formation of the Ghilan, or perhaps the djinn who did not become a part of humanity are the ones that turned that way. Seems that a Ghul would not follow the Word of Elohim (or however I name the overarching religion).
I've dug up a bunch of books on Arabian culture that I'm going to power through in the next few weeks. I'm hoping to take a look at both Persian and Mesopotamian cultural roots too. I'd like for this to work on several levels of culture.
I had a thought regarding removing humanity altogether, and having the world of the djinn be the one played in, but I wasn't sure how happy I was with that, given how I'd like the bad guys to work. We'll see though. Would certainly lend an edge to how people would see the world as different.
As it stands, I think the different djinn are the ones in touch with elemental forces, whilst humanity is able to harness the arcane in both good and bad ways. Piety and prayer will avoid corruption, but there'll be plenty about, from pickpockets and hashish dens to necromancy and demonic bargains.
Also, packs of street rats with different skills, abilities, and skin colours from blue to red to grey are already running around sandy bazaars in my mind.