Arceus-Fairy looks to be a major threat this generation. With key resistances to Fighting, Dark, and Bug, as well as a Dragon immunity and only two weaknesses, FairyCeus can threaten a wide range of Ubers and can fill both a supportive and sweeping role. Lets see some sets (EVs tbd depending on how speed teirs shake out):
Monoattacking
Arceus @ Pixie Plate
Trait: Multitype
-Calm Mind
-Recover
-Substitute/Refresh/Will-o-Wisp
-Judgement
Fairy gets great coverage in Ubers, and as a result Fairyceus can run an excellent mono-attacking set. This set is standard fare for formes such as Water and Dark; however Fairyceus has an advantage of being immune to the STAB Dragon moves of many Ubers, allowing easier set-up. Substitute, Refesh, and the newly buffed Will-O-Wisp all serve a purpose to shield Fairyceus from status and Leech Seed, heal status, and cripple physical attackers respectively. This set should run maximum HP and a lot of Defensive EVs, although speed may be beneficial as well.
The set is destroyed by Gyro Ball Ferrothorn, Scizor, Steel-Arceus, Poison-Arceus, Fire-Arceus, Iron Head Genesect, Ho-oh, and Heatran. Good partners thus include something that can check these Pokémon, such as a Heatran of your own or Giratina-O.
Offensive Calm Mind
-Calm Mind
-Psyshock/ Thunder/ Recover
-Fire Blast/Focus Blast
-Judgement
With this set, Fairyceus can easily destroy the Pokémon that wall it's STAB. After a single calm mind, most Steel-types are roasted by Fire Blast, while Ho-oh and Arceus-Poison can be KO'd with Psyshock. This set still struggles against fast users of Steel moves like Scizor, Mega Lucario, and Scarf Genesect. Ho-oh also does well if Psyshock is used, and Heatran walls the set if Fire Blast is used over Focus Blast.
Support
-Recover
-Defog / Toxic / Will-O-Wisp
-Stealth Rock / Stone Edge / Thunder Wave
-Judgement
Like most Arceus formes, Fairy Arceus can run a great support set that can check Uber threats like Rayquazza, Giratina and Darkrai. Recover is necessary for recovery, and Judgement to give an offensive presence. The other two moves are a matter of what your team needs, but include Defog to clear hazards, Toxic to cripple opposing Arceus formes, Stealth Rock, Stone Edge for Ho-oh, and Thunder Wave
This set should probably be EV'd specially defensively.
Other notable options:
A Swords Dance set will be very viable if Arceus ends up getting Play Rough, but as of now it is outclassed. Most other options are done better by other Arceus formes.
Also these sets seem a little bit jankey to me, so obviously if you have better ideas please post and I'll add them to the OP