ok, because I have experience with gen8 NDAG and slight experience with gen9 NDAG, ill try and give some feedback, although because NDAG is not a popular tier (Revive Cats, Shedinja, etc ruined it) you can't actually play it on the ladder sooooo
ANYWAYS
Diancie is fine, so first is Caly-S. Dark Pulse with Astral Barrage is incredibly redundant, as Dark and Ghost have the same offensive coverage, with Ghost usually being the preferred offensive type due to near unresisted attacks. Looking at your team, I feel like Sub makes the most sense to replace DP. You have the lefties to facilitate a free Sub when Caly comes in on a defensive Pokemon, so make use of it! If you want to run four attacks, use Tera Fighting or Fairy (I don't have enough experience to prefer one or the other) to hit Dark types and resist their attacks, then use Tera Blast. Fighting handles stuff like Gambit, while Fairy hits Yveltal. I'd recommend Fairy due to Breloom and Zacian already carrying Fighting Attacks, and Yveltal (i think) being more prevelant. I also recommend Psyshock over Psychic, as Astral would blow through everything except for stuff like Clod and Bliss, which Psyshock handles easier due to their lower Defense.
I wanna clarify something here first: You can't Tera a mon holding a Mega Stone and is able to Mega. For example, I can't Tera Ghost my Ttar holding a Tyranitarite. With that out of the way, lets discuss why Breloom is absolute garbage in NDAG. It's frail, it's slow, it gets walled by Shed even without tera, and faster Ghost types (theres a lot: Caly, Gengar-Mega, Marsh, etc) pummel it to death especially without sash. Resisting Diancie's weaknesses mean nothing when a Pokemon is paper thin already. Just because Kartana is a grass type doesn't mean it can eat up beefy Hydro Pumps all day with its 59 HP and 31 SpDef. With that being said, if you want a mon to cover Diancie's weaknesses, I'll go with one of Primal Don or Tera Grass Ho-Oh. The main threat to Mega Diancie is Zacian's faster Behemoth Blade, and Primal Don and Ho-Oh take those all day. Primal Don has the advantage of being a strong wallbreaker/sweeper itself, with access to SD for power and Rock Polish for speed. Ho-Oh is more defensive, having access to reliable recovery, which isn't even necessary due to Regen, and great utility in status and whirlwind. Tera Grass is to prevent Zacian from blowing it up with Wild Charge, although if you put enough attack invest you can just OHKO it with Sacred Fire. If you're incredibly worried about Diancie's weakness, Ho-Oh is the better choice, as it can also take Ground moves while PDon cannot.
Similar to Breloom, Sylveon is useless. It's slow, and while it's not frail, it's power is not up to par against to nuclear warheads of NDAG. If you really want wish support, best you got is Blissey, which isn't bad, but is threatened by Caly's Psyshock, Zacian, and Mega Ray. There really isn't a good cleric mon anywhere in ND currently in the higher tiers, as their passivity tends to make them setup fodder or momentum grabbers. Instead, if you just want a defensive mon, I'll go with a defensive Arceus form, probably Water due to your team. It can provide decent utility by spreading status, hazards, screens, and be a general wall. It isn't as passive as other mons, still packing a decently strong Judgement. It does lack pivoting and any cleric support, however as I said I don't think theres any viable clerics in NDAG.
So Masq can set up webs and pass Quiver Dances. Sure. The question is, why not Smeargle or Ribombee? Smeargle acts a stupidly good lead. It packs Spore, a plethora of support moves, setup moves, and Baton Pass. Its moody ability provides it opportunities to snag an Attack of SpAttack boost, meaning it can pass to either Caly Shadow or Zacian. This is furthur exemplified by the power of Sub, as Smeargle can easily pass a Substitute as well. Ribombee has one notable advantage over both Masq and Smeargle: Speed. It packs Stun Spore for easy status, and it also has QD and BP like Masq. Between the two, Smeagle is definitely better, but if you value Speed (which is unlikely) Ribombee does it better.
Zacian without Behemoth Blade? Bro what are you doing? Behemoth Blade is 20BP stronger than Iron Head! Sacred Sword is generally worse than Close Combat, since Dynamax isn't implemented in Gen 9 ND formats yet and Mons can't snag easy Defense boosts. Zamazenta is also wholly unviable (the fact that base zenta is still NDOU speaks volumes) and overall CC's higher BP makes it the better choice.
Now, back to what I said before. NDAG is not playable on the ladder, however NDUbers, a (slightly) more balanced version, exists. It is possible to shift your team over to NDUbers, and I'll provide movesets and explanations to every change to your team down below.
Caly-Shadow -> Primal Don
Groudon-Primal @ Red Orb
Ability: Desolate Land
Tera Type: Ground
EVs: 252 Atk / 4 SpA / 252 Spe
Naughty Nature
- Rock Polish
- Precipice Blades
- Fire Blast
- Stone Edge
Because Caly-Shadow is banned, I have to replace it. Primal Don is the dominant leader of NDUbers, similar to how Mega Ray acted in NDAG (not counting scummy strategies). Because your team does lack speed boosting options, I opted for a mixed Rock Polish set, however there are more defensive sets available on Smogon which you can go check out if you prefer more stability. I'll provide one here as well:
Groudon @ Red Orb
Ability: Drought
EVs: 248 HP / 56 Def / 204 SpD
Tera Type: Flying
Relaxed Nature
- Spikes
- Precipice Blades
- Stone Edge
- Toxic
This is the standard defensive set on Smogon. Spikes provides the other hazard you may want, Toxic is for bulky mons, and then you got the standard EdgeQuake combo (reincarnated as EdgeBlade).
Breloom -> Ho-Oh
Ho-Oh @ Heavy-Duty Boots
Ability: Regenerator
Tera Type: Grass
EVs: 248 HP / 208 Def / 52 SpD
Impish Nature
- Sacred Fire
- Thunder Wave / Toxic
- Brave Bird
- Whirlwind / U-Turn
As mentioned before, Ho-Oh is the replacement for Breloom. You got your dual STAB to exert some sort of offensive potential, a status move of your choice (I recommend TWave tho) and the choice between phasing out potential setup threats, like Xern, or a pivoting move.
Sylveon -> Arceus-Water OR Xerneas
Arceus-Water @ Splash Plate
Ability: Multitype
EVs: 252 HP / 160 Def / 96 Spe
IVs: 0 Atk
Tera Type: Fairy
Timid Nature
- Judgment
- Ice Beam
- Taunt
- Recover
Arceus-Water is the defensive replacement for Sylveon. Judgement and Ice Beam provide great coverage against the Dragons and Grounds, Taunt is to prevent the most common type of hazard removal, Defog, and Recover is Recover. However, after thinking for a bit, I realized your team may befenit from a bit more offensive pressure.
Xerneas @ Power Herb
Ability: Fairy Aura
EVs: 48 HP / 24 Def / 252 SpA / 184 Spe
Tera Type: Electric / Ground
Timid Nature
- Geomancy
- Moonblast
- Thunder
- Substitute / Hidden Power Ground
A fast special attacker with great late-game potential, GeoXern is known as a premier choice for a cleaner. Substitute can be used to gain value off of switches, but Hidden Power Ground hits PDon super effectively. A Tera of Electric along with Thunder threatens Ho-Oh, while Tera Ground with HP Ground threatens PDon. I would personally go for Tera Ground with HP Ground, as your team lacks a reliable method to deal with PDon at the moment.
Masquerain -> Ribombee
Ribombee (M) @ Focus Sash
Ability: Sweet Veil
Tera Type: Steel
EVs: 248 HP / 8 SpA / 252 Spe
Timid Nature
- Sticky Web
- U-turn
- Stun Spore
- Moonblast / Tailwind
I generally prefer Ribombee over Smeargle outside of NDAG simply due to Moody not being nearly as useful in NDUbers, which banned BP. Ribombee basically does the same things that Masq does but faster, while also providing status in Stun Spore. One option I messed around with a bit is Tailwind, which allows for an immediate speed boost for your team. If you choose to run it, go for a 252HP / 4Atk / 252Spe spread with a jolly nature.
And that's it! This is your newly refined NDUbers team (its obv not perfect, you have to refine it as you test). It still uses the Mega Diancie as a "core" (more so just a component), and is now outfitted with better mons and moves. Have fun playing NDUbers, and I hope you find it as fun as a potential NDAG!
