And here it is! Prism Armor for both forms.
Dusk Mane Necrozma gets an attack boost, whereas Dawn Wings Necrozma gets a special attack boost.
Only the Solgaleo Z and Lunala Z are required to execute the Z Moves each Necrozma form (i.e. no special Z Crystal for each form).
Solgaleo Z turns Sunsteel Strike to Sunshine Smasher (phonetically translated).
Lunala Z turns Moongeist Beam into Moonlight Blaster (phonetically translated).
Both forms get a new move: Photon Geyser (again, just phonetically translated).
They've also improved the Rotom Dex so you can better communicate with it so it'll like you more. Apparently it might even start to become like you depending on your interactions (probably based on your answers to its questions).
You can also receive an item called Rotopon which, from what I can tell, is USUM's version of O-Power, since it says you can get increased experience and money.
If you become good enough friends with your Rotom Dex, it will be able to use Z Rotom Power, which allows you to re-use a Z-Move in battle.