Haven't had much time to play yet, but some returning mons look promising in my opinion, so I'm gonna go though some that I think might be good or at least will see some play (I'm not a qualified source but trust me ok)

Solgaleo @ Venusaurite / Sablenite / Lati@site / Like anything works
Ability: Full Metal Body
EVs: 252 HP / 4 Atk / 252 Def
Relaxed Nature
- Future Sight / Psychic Fangs
- Sunsteel Strike
- Morning Sun
- Teleport
Solgaleo in my opinion feels really good, you're able to check a plethora of stuff like -ate espeeders (can even optimize with stones to have better MU), Eternatus who's returning, Deoxys-Speed not running Shadow Ball, TC Fighting-types like Zapdos-Galar and Urshifu-R and probably more that I'm missing. Idk what offensive sets are good, but im assuming aswell that they're gonna be as good. This set is probably not the best, but there's gonna be a lot of good sets and I'm excited to see this mon. Not sure if it's gonna get restricted tho, but I'll enjoy it for now.

Raikou @ Red Orb
Ability: Pressure
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Weather Ball
- Thunderbolt
- Extrasensory / Volt Switch / Shadow Ball
- Calm Mind
Woo we definetly needed another Red Orb abuser that's even faster than Thundurus! This is probably bonkers in practice, and I'm hoping as a result we can finally ban Red orb instead of banning this, since it's probably meh otherwise. It does lack NP compared to Thundurus, but it's still gonna be unbearable with CM i feel.

Deoxys-Defense @ Gyaradosite
Ability: Pressure
Tera Type: Psychic
EVs: 248 HP / 8 SpA / 252 SpD
Calm Nature
IVs: 0 Atk
- Psycho Boost
- Spikes
- Recover
- Teleport
(Ignore the set im still not sure what I want) A Hazard-setter + Slow pivot with good bulk will surely be decent at least right? Anyways you could probably try a more defensive approach but I expect the Speed-Forme to be much more used, but this could still be a niche option.

Deoxys-Speed @ Cameruptite
Ability: Pressure
EVs: 108 HP / 252 SpA / 148 Spe
Timid Nature
IVs: 0 Atk
- Psychic
- Ice Beam / Thunderbolt / Shadow Ball
- Thunderbolt / Ice Beam / Shadow Ball
- Nasty Plot
This also looks really fuckin' strong, since it's got enough bulk to not instantly melt to -ate Espeed while also outspeeding everything barring Eleki. Something like this is gonna be really hard to check defensively, since NP + SF shreds through most Arceus-formes and Glowking, as well as most other things. It does require setup if u wanna get OHKOes, but it's definetly gonna be good. You could probably invest more in bulk aswell to live +1 Espeed from Dnite, but i'm not an expert at optimising EVs so this will do for me.
Deoxys-Speed @ Gyaradosite
Ability: Pressure
EVs: 96 HP / 252 SpA / 160 Spe
Timid Nature
IVs: 0 Atk
- Psycho Boost
- Taunt
- Stealth Rock
- Spikes
Deoxys-Speed @ Light Clay
Ability: Pressure
EVs: 248 HP / 8 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Reflect
- Light Screen
- Taunt
- Teleport
More Hyper-Offense leads as well, both screens and hazards seems good. I don't think it's entirely outclassed by Screens Eleki thanks to Taunt + Teleport, but HO definetly got something good here imo.

Eternatus @ Black Sludge
Ability: Pressure
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Dynamax Cannon
- Sludge Wave
- Flamethrower / Toxic Spikes / Toxic
- Recover
It's back, and it looks really good from what I can tell. Major nuisance to switch into, great defensive typing to not get blown up, and can annoy Glowking teams with Toxic Spikes if Glowking's their best switch-in. I haven't played with this much when it was legal earlier, but It's definetly gonna be good.