Koraidon @ Life Orb or something (tera Fire)
Jolly 252 Spe 252 Atk
- Collision Course/Close Combat
- Dragon Claw
- Flare Blitz
- U-turn
Miraidon @ Heavy Duty Boots (tera Electric)
Timid 252 SpA 252 Spe
- Electro Drift
- Draco Meteor
- Overheat
- Volt Switch
Kyogre @ Choice Scarf (tera Water)
Timid 252 Spa 252 Spe
- Water Spout
- Origin Pulse
- Thunder
- Ice Beam
Groudon @ Leftovers (tera Ground or Dragon)
Whatever defensive spread ends up being needed, maximally focusing on Attack otherwise
- Stealth Rock
- Spikes
- Precipice Blades
- Dragon Claw
Zacian @ Rusted Sword (tera Dark)
Jolly 252 Atk 252 Spe
- Behemoth Blade
- Play Rough
- Night Slash
- Swords Dance/Close Combat
Calyrex @ Life Orb/Choice Specs (tera Ghost)
Timid 252 SpA 252 Spe
- Astral Barrage
- Psyshock/Psychic
- Pollen Puff
- Substitute/Nasty Plot/Draining Kiss
Calyrex set seems odd but it's because Arceus-Dark will almost certainly replace Yveltal as the main Calyrex check and Pollen Puff is your best option against it. Arceus-Dark is also immune to Trick so you need more direct counterplay. I'm not super convinced Calyrex can afford to be taking loads of chip damage, so Specs might be the play here.
Zacian has Dark tera type so it can function as a Calyrex check -- shaky, but it's the only thing this team has for it and probably relies more on putting enough immediate offensive pressure on the opponent that they don't get any setup opportunities. Night Slash for extra STAB in this scenario and more reliably beating Calyrex, but you might be able to safely forgo it. With Intrepid Sword only working once per battle, it ideally wants to be staying in as long as possible, hence Swords Dance. These are your main wincons. I haven't done the calcs for whether Zacian's stat nerf hurts it enough to make you want to replace it with something else.
Koraidon and Miraidon focus on hitting hard and then pivoting out. Koraidon benefits from a Rock resistance, but Miraidon wants HDB to do its job properly. Tera fire on Koraidon for burn protection, but it's a risk with Rocks unless you run HDB on it aswell. The fact that all three of their combined STABs have common type immunities makes Choice items a massive liability on these two, IMO.
Groudon sits there being bulky and setting hazards, but also puts offensive pressure on. It runs Dragon Claw purely for Giratina-O; it no longer gets Heat Crash, and even if you wanted to run Fire Punch, its overlap with Precipice Blades means it has no relevant targets. Given that this team has no defoggers, you want to be winning the hazards game, so I think it's important that everything can offensively pressure Giratina (the only thing that learns Defog and is even remotely viable.) Groudon still just punches holes with Precipice Blades in the event that your opponent isn't worth playing the hazards game with (e.g. they have loads of mons with HDB on), so I think Tera Ground is the play, but hitting Koraidon and Giratina harder might be something you want to prioritise.
Scarf Kyogre is pretty self-explanatory (running Timid to outspeed Calyrex-S) and still beats face, especially with Tera Water, but I'm not sure how good it will be at its job with Groudon *and* Koraidon everywhere and hazard control options being quite limited. You might want to nix it for Arceus-Dark or potentially Rayquaza to go all-in on VoltTurn as a strategy while pulling double duty as a potential setup sweeper (it's now the only thing that gets Dragon Dance). In theory you can screw Koraidon over by disabling the weather, but in practice this is only really useful if your opponent's Koraidon doesn't have dragon coverage (and depends on whether or not the two new box legends work such that disabling the field effect turns off their stat boosts). Rayquaza is hard to evaluate in this meta because it has a lot of tools but it also has pretty big 4MSS. Tripling up on Dragons seems like it also has the potential to be a massive liability.