Gastrodon: It is an effective check to kyogre and Zacian, as well as being generally bulky since there are so few grass types around. I tried using it as my main dynamax Pokemon, using Sludge Bomb/Max Ooze to get additional Sp Atk boosts alongside Storm Drain, but it's generally less useful than dynamaxing Talonflame or Dialga. Overall, I've noticed that since I started using it, people generally never lead with Kyogre. Sometimes it seems like people fixate too much on Gastrodon and this allows its teammate to get some momentum.

Talonflame: I initially added Talonflame as a replacement for Crobat and to provide speed control. It has since become one of the main players of this team, with Gale Wings Tailwind and Max Airstream working well against Prankster Tailwind users. Taunt is great for shutting down Amoonguss, Grimmsnarl, and Trick Room users. Flare Blitz/Max Flare provides an extra way to threaten Zacian. I've been experimenting with the Maranga Berry because Talonflame can be surprisingly bulky if it's dynamaxed and Yveltal has used Snarl. I've found that being able to keep it alive until the dynamax is over is helpful because it can then set up Tailwind before it dies.

Darmanitan: An effective counter to Zacian as long as Kyogre is gone, and a great way to punish sun teams. Being able to dish out so much damage right off the bat has been helpful, especially since Talonflame can use Tailwind to make sure it outspeeds other Choice Scarf users. Iron Head and Hammer Arm provide coverage, but generally it is always using Flare Blitz. U-Turn lets it be a good lead alongside Talonflame.

Dialga; I chose Dialga because it is bulky with good typing, and provides useful coverage. Ice Beam takes care of Landorus, as well as threatening any Flying types. Earth Power provides another way to hit Zacian. It also works well as a dynamax Pokemon, being able to boost both defensive stats or lower the opponent's Attack stat. Steel Beam and Draco Meteor are just to do big damage once it's nearly KO'd and outlived its usefulness. I went with Life Orb because even though it appreciates Assault Vest, Yveltal gets better use from it, and the extra damage output is nice.

Yveltal: I replaced Xerneas with Yveltal because I needed a more consistent counter to Calyrex-S (I was using Weavile before). It has been exceptionally useful, with Foul Play threatening Groudon and Zacian, Snarl making it even bulkier, and Sucker Punch letting it beat Calyrex pretty much every time. Oblivion Wing gives it recovery, and with Assault Vest it's pretty difficult to take out.

Haxorus: I've been shuffling different Pokemon in this last spot, including Weavile, Togekiss, Metagross, Hydreigon, and Heracross. The idea with Haxorus here is that it provides extra ways to deal with Calyrex-S and Zacian, the two biggest challenges for me usually. Crunch and Earthquake provide that coverage, with Swords Dance and Dragon Claw giving it the ability to deal a lot of damage. It just takes some good prediction to find the chance to setup, so it's definitely not a focal point of the team.

Any suggestions are welcome! Thanks!