I'm not really sure what to think about Dawn Wings. Its typing is shit, speed leaves a lot to be desired even for Ubers standards, and it lacks Lunala's Focus Blast leaving it completely man-handled by Dark types like Banded Tyranitar, Hoopa-Unbound, and Ash-Greninja if it were eventually tested in OU, and Yveltal, Arceus-Dark, and support Tyranitar in Ubers.
However, I'm stunned by how many set up moves Necrozma has. It gets Autotomize and Rock Polish, Calm Mind, Swords Dance, and Iron Defense. Lunala and Solgaleo only had access to Calm Mind, in comparison. The question I have, however, is how is it going to fit these moves, other than CM that is, in to its moveset? I feel this mon would need Moongeist Beam, Photon Geyser, and a coverage move that doesn't let it get dicked by certain Dark types for it to have a chance at succeeding wherever it ends up. It gets Signal Beam....yay? It also gets recovery options in Morning Sun and Moonlight, which is great and all, but Lunala had Roost which has twice the amount of PP.
In theory, DW loves the fact that it gets Iron Defense and Calm Mind at the same time as it would make it substantially bulkier, which would alleviate its weaknesses to a degree. But again, what moves get taken off to accommodate such a combo? Both a mono-attacking set of Iron Defense, Calm Mind, Moonlight and Moongeist Beam/Photon Geyser, and Iron Defense + Calm Mind + two STAB attacks sound terrible and look easily exploitable.
Maybe Rock Polish has a better chance of pairing it with CM for a double dance set? A set I just came up with for OU would look something like this:
Necrozma-Dawn Wings @ Buginium Z / Lunalium Z / Psychium Z
Ability: Prism Armor
EVs: 4 Def / 252 SpA / 252 Spe
Modest Nature
IVs: 0 Atk
- Signal Beam / Psyshock
- Moongeist Beam
- Calm Mind
- Rock Polish
At +1, Savage Spinout OHKOs Banded Tyranitar in sand, and after a Rock Polish boost, Signal Beam itself lets it, without needing to Calm Mind, OHKO (Ash) Greninja after Stealth Rock and OHKO Hoopa-Unbound completely. Psyshock could work as an option to hurt special walls like Chansey harder. Even Mega Sableye can't handle this set very well because Knock Off is a 2HKO vs DW Necrozma, and +1 Moongeist Beam 2HKOs Careful Mega Sableye back, and an unboosted Moongeist Beam will still 2HKO after Stealth Rock anyways.
The big issue with a Rock Polish set is that it's still Sucker Punch food, and mons like Mega Mawile and Bisharp (which I can see rising in usage because of all the new Defoggers entering the tier) could take advantage of it.
I'm not really sure if this set would even be that great, but I guess the point to all this is that I wouldn't call off DW Necrozma as a healthy OU mon just yet, as its movepool looks deceptively good despite not having Focus Blast or even Hidden Power Fighting because of the 3 perfect IVs that legends are guaranteed to now have.