Latios
Latios is just STAB? Wow, that's a waste of coverage. First off, replace both Luster Purge and Psychic with Psyshock, then get rid of either Dragon Pulse or Draco Meteor (I would recommend keeping Meteors, but if you're against the recoil, then Dragon Pulse is still viable). Then add at least one coverage move, probably Ice Beam for one of them, although Defog instead of another coverage move is also a very good option, since your team has no way of dealing with hazards. Next, I would highly recommend running Timid over Modest.
Chansey
You don't have any EVs on your Chansey, which I'm guessing is an oversight. Another thing you don't have on your Chansey is any form of sustainability, which is extremely helpful with stall sets like this. While I understand Psychic to deal with Poison types, it still leaves you at a disadvantage against Steel types, so either way, you're left vulnerable. I think it would be best for this Chansey to fully commit to being as effective of a staller/cleric as it can be, even if that means it has nothing to deal with Steel and Poison types; the rest of the team can deal with that. For that reason, I would recommend replacing Psychic with Wish for the powerful Wishtect combo, making it more effective both at being a staller and a cleric (you'd also need to replace Aromatherapy with Heal Bell, since Wish and Aromatherapy are incompatible on Chansey). After that change, I would recommend the standard spread of 4 HP / 252 Def / 252 SpD Bold, with Natural Cure instead of Serene Grace.
Kyurem
Okay, as a general rule of thumb, don't run two damaging moves of the same type unless they both offer distinct advantages, like one priority and one high damage. One reliable medium damage and one unreliable high damage aren't distinct enough from each other to really justify putting one of each on a moveset, so please choose between either Dragon Claw or Outrage, then replace the other one with Fusion Bolt. Also, I'm not really sure if Noble Roar is a great option; Hone Claws would probably be better.
Metagross
I hate to say it, but please don't use Metagross in OU, especially not like that. First of all, why in the world are you not using Scarf or Band? And, like Chansey it doesn't have any EVs, although that can get a pass since I assume that was a mistake. Although if you really want something that just blows up in your opponents face, I would recommend using something else, since Metagross is extremely low-ladder in UU. Landorus has 10 more Atk, higher speed, Intimidate to negate the lower defense, and huge surprise factor if you're dead-set on explosion-only, since most people want to do more with their Landos. Although I would recommend at least also U-Turn:
Landorus @ Choice Band
Ability: Intimidate
EVs: 252 Atk / 4 Def / 252 Spe
Adamant/Jolly Nature
- Explosion
- U-Turn
- some other moves, idk, I don't usually play any tiers that allow it. EQ, probably.
That being said, Landorus has so much more it can offer your team. While U-Turn on this set still gives you a great pivot, Stealth Rocks is considered one of the most useful moves in the entire game, and not without reason. But if you really want just raw Explosion, then I guess running such an unorthodox set allows you to play it like a lure and catch people off-guard, although, Explosion is run on roughly ~20% of Landos, so I'm not sure how much success you'll find trying to surprise your opponent into a misplay.
Kartana
Replace Brick Break with something else. Other than that, Kartana looks good.
Heracross
Replace Brick Break with Close Combat and Megahorn with some other coverage move, possibly Bullet Seed or Earthquake. Other than that, Heracross looks good.
Good luck and happy battling :)
