Groudon
Precipice Blades and Earthquake is not a good idea. You really need a Rock type move for mons like Ho-Oh, so Earthquake should go. You have no Dynamax abusers either, and Groudon is one of the best ones, however the Dynamax Groudon set is different from your current set.
Groudon @ Life Orb
Ability: Drought
EVs: 252 Atk / 4 Def / 252 Spe
Jolly Nature
- Precipice Blades
- Stone Edge
- Aerial Ace
- Swords Dance
Cinderace
I don't see the point in this. The moveset is very strange, and Cinderace itself is a strange pick when you have much, much better picks in the metagame. This slot can either go to Kyurem-White or Specially Defensive Yveltal to counter either Kyogre or Calyrex-Shadow, some of the most dangerous and popular Pokemon in the tier.
Kyurem-White @ Utility Umbrella
Ability: Turboblaze
EVs: 36 HP / 40 SpA / 216 SpD / 216 Spe
Timid Nature
- Sheer Cold
- Fusion Flare
- Roost
- Freeze-Dry / Dragon Tail
Yveltal @ Heavy-Duty Boots
Ability: Dark Aura
EVs: 252 HP / 4 Def / 252 SpD
Careful / Calm Nature
- Snarl / Knock Off
- U-turn
- Roost
- Defog
Eternatus
Why are you using Dragon Dance with no Physical attacks? It is a completely pointless move to have on it, Recover should be used instead. Imo Toxic > Toxic Spikes, as Tspikes don't hit Ho-Oh and Yveltal while Toxic does. Outside of that it looks fine to me.
Zacian-Crowned
If you choose to keep Zacian, Close Combat should be used over Sacred Sword, and if you use Play Rough, you'll lack options for Ho-Oh and Kyogre, so I'd suggest Wild Charge there. You can also replace Zacian with Necrozma-Dusk Mane
Necrozma-Dusk Mane @ Leftovers / Rocky Helmet / Heavy-Duty Boots
Ability: Prism Armor
EVs: 252 HP / 252 Def / 4 SpD
Impish Nature
- Sunsteel Strike
- Thunder Wave / Toxic
- Morning Sun / Moonlight
- Stealth Rock / Knock Off
Dracovish
Kyogre is one of the best Pokemon in AG while Dracovish is not very good. Kyogre has many options to choose from such as Calm Mind, Sheer Cold, Choice Specs, Choice Scarf, Block+Rest, etc, while Dracovish is pretty much stuck to Choice Band.
Kyogre @ Choice Specs / Choice Scarf
Ability: Drizzle
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Water Spout
- Origin Pulse
- Ice Beam
- Thunder
Kyogre @ Leftovers
Ability: Drizzle
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Scald
- Block
- Rest
- Calm Mind
Kyogre @ Leftovers
Ability: Drizzle
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
- Scald
- Sheer Cold
- Rest
- Sleep Talk
Magearna
If you're going to be using Magearna at all for some reason you'd use it as a Xerneas counter, but Necrozma-DM does that better. If you have Dusk Mane on your team already, you should use Kyurem-White if you chose Yveltal and Yveltal if you chose Kyurem-White.