We can see from the trailers that Necrozma will be fought at the Poni Altar in its Dusk Mane/Dawn Wings form, on top of seeing snippets of the cutscene where Nebby evolves from Cosmoem and is accosted and assimilated by Necrozma.

With B2W2, Kyurem cannot be caught in its Black/White form for the in-universe reason being Ghetsis' cane jammer, and the technical reason being due to the same issue with Reshiram and Zekrom that prevents Kyurem from being traded when combined.

What's the deal here - will Necrozma have to be captured while combined with Nebby, and will it be inseparable, or will it be like Kyurem in which it can't be caught in this situation? Or could they do something like have Necrozma be captured, but then revert to normal later in the story before you're able to control its form changes and have Nebby be battled afterwards?