(Briefly answering these to prevent spoilers)

"What's the Nigredo Phenomenon?"

Mutation of the Pokerus that causes the affected Pokemon to take on a primarily black color with a secondary (or in select cases - tertiary) color scheme. Based on the real life melanism phenomenon. They're much stronger than the average Pokemon, on par with those found in Ultra Space, but they're more unruly and the conditions for raising them are stricter. They're often seen as "Harbingers of Misfortune" since, like Absol, shit hits the fan real quick whenever one's around. But only when Elio masterfully uses them throughout his journey does their negative reputation steadily dissipate, becoming more desirable in the eyes of trainers and collectors alike. Such that special regulations and programs had to be created for proper usage and care.

"I adore the nicknames you've given Elio's Pokemon. How did you come up with them?"

Random name generator or variation of a deity's name.

"I have to know the lore of the five Unovan Royal Families!"

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"OMG U BROUGHT BACK NEW TORK CITY FROM THE ANIME MOVIE YES"

It's underutilized as both a concept and a location. So it's best to layer that with Black City to give it more development room while expanding on futuristic themes associated with it.

"Hold up, u mean to tell me once Elio contracts with Ziodyne, New Tork City is overlayed with black city? SO AWESOME! (big black city fan)"

In this continuity, Black City and White Forest are interconnected with Zekrom and Reshiram. Zekrom represents the future, night, idealism, the artificial, and progression. Black City's an amalgamation of these concepts - consistently evolving to reflect both the contractor's state of being while subtly influenced by the advancements made by its new denizens. On the other hand, Reshiram represents the past, day, pragmaticism, the natural, and stagnation. Ergo, White Forest's an also an amalgamation that's unchanging and preserves its natural beauty by any means - producing only what's necessary. It should be noted that the overlay cause these locations to be their own worlds like Ultra Space Pocket Dimensions, yet still physically connected to Unova. The rules of these two locations are vastly different to anywhere else.

"Not related to Elio's lore, but do you think Elio would catch - or at least be interested in - an Aevian Volcarona?"

Elio has one and his name is Metashan: a combination of the Angel Metatron and Pushan - one of Surya's various names in Hindu Mythology.