Take this as a grain of salt as I don't play Gen 7 Ubers (played a little with my alt but stopped playing after I saw a Clefairy). But, I do play Gen 7 AG, and uhh, even though these ain't alike, AG only ha.. nvm leave it.
Ok so, the team looks almost fine, but maybe a few changes are needed.
Problems with the Team:
A few of the sets have somethings to change. For example, Outrage on Mega Mence ain't really required. And uh Marsh seriously looks like a meme...
Diffrent Playstyles against this Team:
Hyper Offense: HO won't really have much problem in breaking through the team, seeing that you are using some of the cookie-cutter 252 / 252 spreads on some Pokémon who would require some better spreads, so as to have more firepower, and bulk. HO's obvious Pokémon, Mega Mence, would have absolutely no problem in breaking the team when Marsh's Sash would be broken, and, seeing that you have no Defogger, that would be very much obvious.
Bulky Offense: Bulky Offense teams usually carry Pokémon like Zygarde, which can really clap your team if it's got a few Dragon Dances. The main problem would be the Glare set, as it can Glare, then setup a Sub, and then proceed to Dragon Dance. Hex Gengar with Will-O-Wisp can try to be smart and WoW you if they expect something like a Marsh switch-in. And then Hex is history.
Balance: Balance would have their own way in countering this team. Team's with Scarf Ho-Oh would able to pick off weakened threats, and Sacred Fire would cripple Extreme killer, as well as Marshadow, with a burn (50% chance good). Leech Seed-Chople Berry Ferro would also irritate you, especially when the PDon is down. And, if you try to be smart and setup Arceus on something like a PDon, they sometimes, especially on Balance and BOff builds, carry Roar. Hehe.
Stall: Lol you don't have a stallbreaker glhf. Buzzwole survives almost all Physical attacks from this team, bar the Fire Punch from Don, and Mega Mence. Ho-Oh, and Lugia, make for good Special Walls, and Blissey would be there to wall POgre. As Stall teams also have Phazers, setting up would be a problem for you, especially on Ho-Oh, Lugia, and Mega Sablye also, they spread burns. Stall is really gonna force you out. Even though this is a valid argument that Marsh may break through Blissey and Lugia's, Buzzwole and Mega Sab stop it at it's tracks. Use Taunt Yvel as a stallbreaker if ever needed.
1. Primal Kyogre: This is more or less the "Standard" Calm Mind set, as you also mentioned before. But, the thing this is missing is the great lord, Water Spout. Spout almost obliterate every switch-in that isn't named PDon. Even Pokémon that resist Water, also take loads of damage because of Primoridial Sea. Take, for example, Ferrothorn, it also almost get's 2HKO'd in return when it tries to come in on a WS (252 SpA Kyogre-Primal Water Spout (150 BP) vs. 252 HP / 252+ SpD Ferrothorn in Heavy Rain: 153-180 (43.4 - 51.1%) -- 5.1% chance to 2HKO after Stealth Rock and Leftovers recovery). Now, where to fit WS? You can remove CM and put Spout, if you don't find yourself clicking CM much. Otherwise, what Smogon recommends is to remove Thunder. If you ask me, I'll remove CM, as it's a bit problematic, especially when the opposing PDon is alive and kicking. It's upon ya really. Otherwise, it looks a great Poké.
Kyogre-Primal @ Blue Orb
Ability: Primordial Sea
EVs: 16 HP / 252 SpA / 240 Spe
IVs: 0 Atk
- Water Spout / Calm Mind
- Origin Pulse
- Ice Beam
Spout is the God, Thunder to hit WaterCeus, some Flying Types (names unown to me sadly..) like Yveltal and all, whilst OPulse is after you come down to 40% HP or something, Ice Beam hit's Mega Mence who would be stupid if they stayed in.
2. Arceus: EKiller Arc is great for a late-game sweep, or even as a wallbreaker. This set is also more or less good, but I didn't understand what's Substitute there for. Like, what I do understand is that it would let you setup easily, but yo, this set is hard-walled by Coil Xyg (+2 252+ Atk Arceus Extreme Speed vs. 252 HP / 252+ Def Zygarde: 171-202 (40.7 - 48%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery). They can make some great setup fodder from the Arc, Glare it, setup a few Coil's, taking as less as 20% after 2, and then boom they TArrows everything (but uhhh Marsh needs to be fainted for a sweep, same goes to Darkrai, as it's.. HYPNO HAX). And so, I'd say replace Sub with Ice Beam, Naughty Nature, and 4 SpA EV's, so as to get a 2HKO on Defensive Xyg, and also the 2HKO on Defensive Mega Mence (4 SpA Arceus Ice Beam vs. 252 HP / 4 SpD Zygarde: 316-376 (75.2 - 89.5%) -- guaranteed 2HKO after Leftovers recovery).
Arceus @ Leftovers
EVs: 236 HP / 252 Atk / 4 SpA / 16 Spe
- Swords Dance
- Extreme Speed
- Ice Beam
SD is setup, ESpeed is something you need, Quake is for PDon's and NDM's, Ice Beam is given by me (swagg)
3. Marshadow: Swagger won't work when you reach 1500's. They very well would know to "switch" after you do a Swag.
I'd say go for Life Orb 100%, as you won't like to trade firepower for a strat that ain't gonna work. Marshadow performs best late-game when the opponent's checks to it are weakened and in KO range. Otherwise, Marshadow struggles to avoid being revenge killed by Pokemon that can survive its attacks.
This is especially true when opposing Pokemon like Arceus-Fairy and Toxapex are still healthy — they can come in to easily take hits while wearing down Marshadow through Life Orb damage and robbing your team of any momentum.
Marshadow @ Life Orb
EVs: 252 Atk / 4 SpA / 252 Spe
- Close Combat
- Spectral Thief
- Shadow Sneak
- Hidden Power [Ice]
Combat is so that you can come close to the Pokémon and see what item they holding yis yis yis yis.
Sry I dozed off...
Combat is great STAB, SpecThief is classic, Sneak is prio + revenge killing, HP Ice is for Zygarde's, and Mega Mence's.
4. Darkrai: Oh god we are on the fourth only like I take so much time and nvm tho.
Darkrai is outclassed in Gen 7. In ORAS, it was really OP, seeing Dark Void still had 80% accuracy. Now, with Hypnosis, it isn't that reliable. I'd say just replace it, with LO Yveltal. That, is an extremely good wallbreaker, and also one of the few Pokémon who can 2HKO SuportCeus forms with Dark Aura boosted Dark Pulse (ones that don't resist only do NOT try to 2HKO FairyCeus with DP pls). It also may perform a late game sweep or things like that.
Yveltal @ Life Orb
Ability: Dark Aura
EVs: 4 Atk / 252 SpA / 252 Spe
- Dark Pulse
- Oblivion Wing
- Sucker Punch
DPulse is obvious, Oblivion Wing is good STAB, that also heals gradually. Taunt is to stop the opposing leads (you can use this as a lead and such), and it also stops the usage of Status moves against the team. Also, a plus point is that it's also a great Stall answer, especially after Mega Sab has fainted, as it can Bounce back the Taunt. Sucker Punch is revenge killing + Prio.
5. Mega Mence: The set, it's good, with just some problems. First, don't use Outrage. Xerneas exists. Replace it with Roost. Also, you can replace Return with Double Edge or Facade, as the former has more power, and Facade helps with Burns. Or, an alternate option would be to keep both, and remove Quake. The final decision is upon ya, I can just guide you.
Salamence-Mega @ Salamencite
EVs: 40 HP / 252 Atk / 216 Spe
- Dragon Dance
- Facade / Earthquake
The extra 4 EV in Spe is used to outpace the opposing Salamence if it happens to come in with Intimidate and proceed to set Dragon Dance; Salamence can set its own Dragon Dance nullifying its attack drop and damage it with Double-Edge which should put in KO range for Shadow Sneak and Extreme Speed or self-KO from the opposing Mega Salamence’s Double-Edge. 252 EVs in Atk to maximise its damage output and the rest in HP in increase its all-around bulk slightly.
6. Primal Groudon: The set is more or less usable, but I'd say replace it with some other, as 252 HP / 252 Atk ain't gonna work. Thunder Wave is also rarely used on PDon's (less than 4% usage). As this is your lone Geomancy Xern counter, I'd say if you do wanna keep TWave, it's good, but it's outclassed by other options, such as Swords Dance.
Groudon @ Red Orb
EVs: 136 HP / 168 Atk / 52 SpD / 152 Spe
- Stealth Rock
- Swords Dance
- Precipice Blades
- Rock Tomb / Stone Edge
Smogon's sample set, pretty great. Stealth Rock is Rocks, Swords Dance, when combined with Stealth Rock, allows this Primal Groudon variant to be both a utility entry hazard setter and a wallbreaker at the same time against Defog users such as support Arceus formes, Giratina, and Ho-Oh that would try to remove Stealth Rock.
Precipice Blades is capable of 2HKOing typical support Arceus formes such as Arceus-Water, OHKOing them at +2.
Rock Tomb targets switch-ins like Ho-Oh, Lugia, and Mega Salamence, while also slowing all Arceus formes down to the point where Primal Groudon can strike them first. This, along with the threat of a boosted Precipice Blades, heavily limits their ability to use Defog on Primal Groudon.
Stone Edge is a stronger Rock-type move that proves beneficial against Giratina-O and Mega Salamence and has the power to OHKO defensive Ho-Oh at the cost of lacking a method to slow Arceus formes and other faster Pokemon.
Hope I helped!
PS: You still don't have a Defogger. Choose one from here, I personally prefer.. w8 lemme check VR..
GroundCeus is A+, DarkCeus, FairyCeus, WaterCeus are A, so.. choose..