Ok, so I'm going to try to give you some good suggestions.
First, we're going to have to change the composition of the team. I can see that you are running balance. You have a defensive pokemon in Ho-Oh, and..physical eternatus. Moving SWIFTLY on, I suggest using the core that is quite common and powerful: Specially defensive Eternatus, Physical necrozma dusk mane and defensive yveltal. Also, you need something to deal with groudon and zekrom. I suggest lunala for this. Here are the sets for the boys. Ok, so Ho-Oh isn't very common at all. It doesn't have good synergy with other defensive mons. Galarian Darmanitan isn't a good offensive 'mon. Marshadow doesn't really suit your team imo.
Eternatus @ Black Sludge
Ability: Pressure
EVs: 252 HP / 212 SpD / 44 Spe
Timid Nature
- Dynamax Cannon
- Flamethrower
- Toxic
- Recover
Eternatus is one of the best special sponges in this game. Resisting kyogre's water spouts is nothing to scoff at. It can deal with almost all variants of kyogre, other than sheer cold kyogre. It can threaten many pokemon with a mystical fire, dynamax cannon or a flamethrower. It can cripple walls that are coming in too. @Ignis Aqua Herba helped with this :)
Lunala @ Heavy-Duty Boots
Ability: Shadow Shield
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Ice Beam
- Will-O-Wisp
- Hex
- Roost
Lunala is the definitive answer to many physical set up sweepers, such as dragon dance zekrom and groudon. With will-o-wisp, it can cripply physical attackers. Hex does a lot of damage with the burns. Roost recovers shadow shield, which is insane because it lets it survive a water spout with more than half, letting it roost off the damage. Ice beam covers groudon and zekrom supereffectively.
Yveltal @ Heavy-Duty Boots
Ability: Dark Aura
EVs: 252 HP / 4 Def / 252 SpD
Careful Nature
- Knock Off
- U-turn
- Defog
- Roost
Yveltal is one of the best defoggers in gen 8 ag. First, its typing allows it to stave off earthquakes from necrozma dusk mane, psychics and psyshocks from calyrex-s, and it has good utility in u-turn and knock off. Roost helps it staly alive. It does great against special yveltal, which is a very common threat. Knock off hits Eternatus and the Chansey line HARD.
Necrozma-Dusk Mane @ Rocky Helmet
Ability: Prism Armor
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Stealth Rock
- Sunsteel Strike
- Knock Off
- Morning Sun
Necrozma dusk mane is one of the best checks to zacian, easily the most dangerous physical wallbreaker in gen 8 ag. It is obscenely bulky with prism armor, and it already has a very good attack stat, so even without investment, it can do a crapton. Knock off is used to cripple walls, and to annoy pokemon like boots yveltal.
Now, you need two attackers. Zacian is a good attacker, so I would use it. However, your set needs some tweaking. Here is my updated version:
Zacian-Crowned @ Rusted Sword
Ability: Intrepid Sword
EVs: 4 HP / 252 Atk / 252 Spe
Adamant Nature
- Behemoth Blade
- Wild Charge
- Close Combat
- Assurance
Zacian is an amazing wallbreaker. Steel fairy is an amazing defensive typing, and along with zacian's bulk, it can take some insane hits. Behemoth blade is...self explanitory. It is good stab with an added bonus of punishing dynamax. With wild charge, it can threaten yveltal and kyogre, along with the rarer but still threatening ho-oh and lugia. Close combat is really good to beat up ndm, and assurance, while interesting, can do some really good damage on a switching in necrozma dusk mane. It can also check xerneas very well.
Calyrex-Shadow @ Life Orb
Ability: As One (Spectrier)
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Astral Barrage
- Nasty Plot
- Psyshock
- Draining Kiss
Now, here is the horse. It can destroy defensive yveltal after a nasty plot with a max starfall, and it can destroy balance. Fun fact: Balance is the most common archetype! Yes, it has a horrible movepool, however it can dish out pain with draining kiss and astral barrage. Balance teams are using 'mons like zygarde, Kyurem White, Eternatus, NDM, Ho-Oh, Lunala and Yveltal, all of which the horse massacres. Watch out for ditto, sucker punch yveltal or scarf caly.
Credit to PrimordialSea for guiding me through this and making sure I'm not a fricking idiot.
Hope I helped :)
Here's the paste
