I came to the same conclusion about the Orianna/Heimerdinger comparison, but especially Orianna since Azir looks to have some pretty punishing autos, and can manipulate the positioning of his units.
These are my completely ungrounded assumptions based on the skill showcase videos: I'm assuming he'll have relatively short-medium cooldowns on his Q, since that's used to reposition his soldiers (kind of how Orianna manipulates the Ball), and also on his W, since that's used to summon soldiers in the first place (I'm assuming it'll be somewhat similar to Syndra's Q). With that in mind, the soldiers do disappear after a short while, so I'm guessing it'll be similar to Syndra's Q; you typically won't have more than 1-2 soldiers on the field at any given time. His E cooldown will probably be long, since it's a pretty potent movement ability with CC to boot, and he's a champion that revolves around position control as oppose to just dashing all over the place. His ult cooldown will probably be decently long, since it's a pretty potent disengage/engage ability. Of course, his cooldowns might need to be a little longer than you'd typically see, since his passive encourages him to rush 40% CDR as soon as possible.
I'm thinking his passive is to convert CDR into AS because he's supposed to be sort of a mage champion, meaning CDR is highly valuable, but also he deals damage largely through auto attacks, so AS is very valuable. With this in mind, I'm assuming 21-9-0 masteries and Nashor's Tooth + Banner of Command for 40% CDR, attack speed, and the minion/pet/soldier buff. Also that probably a Lich Bane or Trinity Force, depending on if he's more AD based or AP based, would be good on him. He certainly doesn't seem like a burst mage, so I sort of want to build him as sort of an AP bruiser type; Nashor's Tooth + 5% CDR masteries + Ionian Lucidity Boots -> Tank, of course we'll probably have to wait to see his stats before anything becomes definite. Based on the skill videos, his mana costs didn't seem too oppresive, so I don't think he'd go for the standard mage build (Athenes, Deathcap, Void Staff), but I could be mistaken.
Of course, this is assuming he even has AP ratios (I mean, he's described as a mage, so I think it's safe to assume). If he's AD based, you could see something like Zephyr, Lucidity Boots, Brutalizer -> Youmuu's or something. I wonder, since he is a ranged mage (his autos are ranged when he doesn't have a soldier), how something like Runaan's might work with his soldiers.
I don't know about the ult blocking projectiles as well; it seems a bit too powerful, but since they already have the tech for it (Yasuo and Braum), it could happen. Plus, it's an ult, not a basic ability like Yasuo/Braum/Anivia, so it can afford to be more powerful.
Lore-wise I just assumed he was related to Nasus, especially since they seem inspired by Egyptian Gods. Your interpretation makes more sense though; maybe Azir came because Xerath became sort of popular in the meta and he needs to shut him down :P
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