As for your conclusion, you said it yourself, most of Diancie's checks are Water, Steel, or Ground type pokemon. Those are only 3 types out of 18 but what of the other 15 types? I would be more inclined to agree with you if you were show that every type has a solid counter to Diancie that is optimal for the team (this does NOT mean Scarf Hydreigon with Flash Cannon btw). Scizor is most definitely a check to Diancie as, bar HP Fire, it can switch into anything that Diancie has to throw at it. Celesteela is in the same boat. However, with the rest of your checks, they can't reliably switch into Diancie. Krookodile gets ko'd by Moonblast, as does Keldeo, while Manaphy gets 2 shot by it. These are REVENGE KILL checks, at best, not SWITCH INS. If anything, this may be an indication that maybe Diancie is unhealthy for the Meta if it can generally only be revenge killed rather than switched in on.
Apologies in behalf posting irrevelant / useless calcs. I should've probably posted this for every type and evaluate the situation more carefully. It is my first time posting somewhere and I was a bit nervous. Thanks for the correction.
Normal :
There will be always a scarf ditto to outspeed it. Just posting one basic calc to see it.
252 SpA Diancie-Mega Earth Power vs. 0 HP / 0 SpD Diancie-Mega: 212-250 (87.9 - 103.7%) -- 25% chance to OHKO
252 SpA Diancie-Mega Earth Power vs. 0 HP / 0 SpD Diancie-Mega: 212-250 (87.9 - 103.7%) -- guaranteed OHKO after Stealth Rock
252 SpA Diancie-Mega Earth Power vs. 0 HP / 0 SpD Diancie-Mega: 212-250 (87.9 - 103.7%) -- guaranteed OHKO after 1 layer of Spikes ( If any crazy people uses spikes diggersby or smeargle )
There are
chansey and
porygon 2 to outstall with recovery moves.
0 Atk Diancie-Mega Diamond Storm vs. 248 HP / 252+ Def Eviolite Chansey: 216-255 (30.7 - 36.2%) -- 54.5% chance to 3HKO
252 SpA Diancie-Mega Moonblast vs. 248 HP / 8 SpD Eviolite Chansey: 115-136 (16.3 - 19.3%) -- possible 6HKO
Chansey Seismic Toss vs. 0 HP Diancie-Mega: 100-100 (41.4 - 41.4%) -- guaranteed 3HKO
252 SpA Diancie-Mega Moonblast vs. 252 HP / 0 SpD Eviolite Porygon2: 127-150 (33.9 - 40.1%) -- guaranteed 3HKO
0 Atk Diancie-Mega Diamond Storm vs. 252 HP / 252+ Def Eviolite Porygon2: 84-100 (22.4 - 26.7%) -- 26.9% chance to 4HKO
0 SpA Porygon2 Ice Beam vs. 0 HP / 0 SpD Diancie-Mega: 62-74 (25.7 - 30.7%) -- guaranteed 4HKO ( Bolt does same damage)
The 2 defensive pokemons can switch into it pretty much freely and outstall with recover. Ditto here just revenge kills it with choice scarf set, also threathening diancie in all aspects in terms of boosting. If ditto manages to switch in a boosted mega diancie, it can pretty much sweep the rest of team or get at least 2-3 more pokemons with it.
Flying :
Celesteela. I posted this one's calcs above but reposting here just to show more detailed.
0 Atk Diancie-Mega Diamond Storm vs. 252 HP / 4 Def Celesteela: 159-187 (39.9 - 46.9%) -- guaranteed 3HKO after Leftovers recovery
252 SpA Diancie-Mega Moonblast vs. 252 HP / 252+ SpD Celesteela: 65-77 (16.3 - 19.3%) -- possible 8HKO after Leftovers recovery
252 SpA Diancie-Mega Hidden Power Fire vs. 252 HP / 252+ SpD Celesteela: 110-130 (27.6 - 32.6%) -- 74.6% chance to 4HKO after Leftovers recovery
Calcs of standart spdef celesteela is above. It can pretty much freely switch into any diancie set and manage to 1 shot it.
0 Atk Celesteela Heavy Slam (120 BP) vs. 0 HP / 0 Def Diancie-Mega: 480-568 (199.1 - 235.6%) -- guaranteed OHKO
Skarmory is not a counter but checking well the non hp fire diancies.
0 Atk Diancie-Mega Diamond Storm vs. 248 HP / 252+ Def Skarmory: 93-109 (27.9 - 32.7%) -- guaranteed 4HKO
252 SpA Diancie-Mega Moonblast vs. 248 HP / 8 SpD Skarmory: 120-141 (36 - 42.3%) -- guaranteed 3HKO
252 SpA Diancie-Mega Hidden Power Fire vs. 248 HP / 8 SpD Skarmory: 204-240 (61.2 - 72%) -- guaranteed 2HKO ( Cant switch in)
0 Atk Skarmory Iron Head vs. 0 HP / 0 Def Diancie-Mega: 268-316 (111.2 - 131.1%) -- guaranteed OHKO
Dragon :
No dragon type can switch into moonblast / diamond storm freely.
Bug :
All variants ( Bulky , Mega , Band ) scizors proceeds to oneshot diancie with bullet punch . It can also switch into most of its moves freely except for hpfire.
Forretress. This is another soft check that can switch into diancie that doesnt carry hpfire.
252 SpA Diancie-Mega Earth Power vs. 252 HP / 0 SpD Forretress: 174-205 (49.1 - 57.9%) -- 59% chance to 2HKO after Leftovers recovery
0 Atk Diancie-Mega Diamond Storm vs. 252 HP / 252+ Def Forretress: 93-109 (26.2 - 30.7%) -- 4% chance to 4HKO after Leftovers recovery
252 SpA Diancie-Mega Moonblast vs. 252 HP / 0 SpD Forretress: 137-162 (38.7 - 45.7%) -- guaranteed 3HKO after Leftovers recovery
4 Atk Forretress Gyro Ball (76 BP) vs. 0 HP / 0 Def Diancie-Mega: 280-336 (116.1 - 139.4%) -- guaranteed OHKO
Grass :
Venusaur Mega
Switchs into anything but psychic. Full spdef venusaur fails to get a kill with a giga drain, if you run mixed saur it is a roll for 2 hko.
252 SpA Diancie-Mega Psychic vs. 248 HP / 252+ SpD Venusaur-Mega: 146-174 (40.2 - 47.9%) -- guaranteed 3HKO
252 SpA Diancie-Mega Hidden Power Fire vs. 248 HP / 252+ SpD Thick Fat Venusaur-Mega: 50-60 (13.7 - 16.5%) -- possible 7HKO
252 SpA Diancie-Mega Moonblast vs. 248 HP / 252+ SpD Venusaur-Mega: 57-68 (15.7 - 18.7%) -- possible 6HKO
0 Atk Diancie-Mega Diamond Storm vs. 248 HP / 0 Def Venusaur-Mega: 136-162 (37.4 - 44.6%) -- guaranteed 3HKO
Ferrothorn .
No need calcs for this. Both gyro ball and power whip can 1 shot diancie from full hp. Homewer cannot switch into hpfire.
Dark :
Tyranitar . Only pokemon that can actually switch into diancie under specific circumstances that we dont see often in monotype.
252 SpA Diancie-Mega Moonblast vs. 252 HP / 0 SpD Assault Vest Tyranitar in Sand: 162-192 (40 - 47.5%) -- guaranteed 3HKO
Ground :
Not doing this since anything can pretty much oneshot diancie in this type.
Dragon :
Goodra can barely switch into mega diancie.
252 SpA Diancie-Mega Moonblast vs. 252 HP / 0 SpD Assault Vest Goodra: 170-204 (44.2 - 53.1%) -- 23.4% chance to 2HKO
0 Atk Goodra Iron Tail vs. 0 HP / 0 Def Diancie-Mega: 268-316 (111.2 - 131.1%) -- guaranteed OHKO
Ice :
Nothing can switch into mega diancie safely, everything is either OHKO or 2HKO.
Electric :
Only mon to switch in freely is air balloon magnezone if ever it switches into an earth power.
252 SpA Diancie-Mega Earth Power vs. 132 HP / 0 SpD Magnezone: 500-592 (159.2 - 188.5%) -- guaranteed OHKO
252 SpA Magnezone Flash Cannon vs. 0 HP / 0 SpD Diancie-Mega: 484-576 (200.8 - 239%) -- guaranteed OHKO
Fairy :
Klefki.
Can pretty much switch in freely, can set up screens easily .
252 SpA Diancie-Mega Earth Power vs. 252 HP / 252+ SpD Klefki: 180-214 (56.6 - 67.2%) -- guaranteed 2HKO after Leftovers recovery.
252 SpA Diancie-Mega Earth Power vs. 252 HP / 252+ SpD Klefki through Light Screen: 90-107 (28.3 - 33.6%) -- 98% chance to 4HKO after Leftovers recovery
Unless a player gets a double max roll, klefki is 3HKO in case of a switch. That gives good opportunity to other teammates for a revenge kill.
Mimikyu.
While disguise is active, it can always switch into mega diancie. But cant get any significant damage up .
252 Atk Life Orb Mimikyu Play Rough vs. 0 HP / 0 Def Diancie-Mega: 138-164 (57.2 - 68%) -- guaranteed 2HKO
0 Atk Diancie-Mega Diamond Storm vs. 0 HP / 0 Def Mimikyu: 195-231 (77.6 - 92%) -- guaranteed 2HKO
252 SpA Diancie-Mega Moonblast vs. 0 HP / 4 SpD Mimikyu: 174-205 (69.3 - 81.6%) -- guaranteed 2HKO
Poison :
Weezing . Immune to earth power, takes low damage from diamond storm / hpfire and moonblast. Cant switch into psychic homewer.
252 SpA Diancie-Mega Moonblast vs. 252 HP / 0 SpD Weezing: 121-143 (36.2 - 42.8%) -- 97.2% chance to 3HKO after Black Sludge recovery
0 Atk Diancie-Mega Diamond Storm vs. 252 HP / 148+ Def Weezing: 111-132 (33.2 - 39.5%) -- 18.7% chance to 3HKO after Black Sludge recovery
No other poison type can switch into diancie without getting 2HKOed.
Fighting :
No fighting pokemon can switch into diancie's moonblast.
Psychic :
Bronzong . Best option for psychic to switch into diancie mega. Gyroball is guaranteed hit, immune to earth power, resists diamond storm, psychic and moonblast.
0 Atk Bronzong Gyro Ball (126 BP) vs. 0 HP / 0 Def Diancie-Mega: 456-540 (189.2 - 224%) -- guaranteed OHKO
0 Atk Diancie-Mega Diamond Storm vs. 252 HP / 4 Def Bronzong: 72-84 (21.3 - 24.8%) -- possible 6HKO after Leftovers recovery
252 SpA Diancie-Mega Moonblast vs. 252 HP / 252+ SpD Bronzong: 59-69 (17.4 - 20.4%) -- possible 7HKO after Leftovers recovery
Metagross . Slightly spdef invested metagross can switch into freely with the help of shuca berry and kill it with bullet punch .
252 SpA Diancie-Mega Earth Power vs. 236 HP / 0 SpD Shuca Berry Metagross: 125-148 (34.7 - 41.1%) -- guaranteed 3HKO
252 SpA Diancie-Mega Earth Power vs. 236 HP / 0 SpD Metagross: 250-296 (69.4 - 82.2%) -- guaranteed 2HKO
96+ Atk Metagross Bullet Punch vs. 0 HP / 0 Def Diancie-Mega: 244-292 (101.2 - 121.1%) -- guaranteed OHKO
Wishpass jirachi.
Capable of tanking earth power and outstall with wishspam and oneshot it with iron head.
252 SpA Diancie-Mega Earth Power vs. 248 HP / 204+ SpD Jirachi: 172-204 (42.6 - 50.6%) -- guaranteed 3HKO after Leftovers recovery
0 Atk Jirachi Iron Head vs. 0 HP / 0 Def Diancie-Mega: 316-376 (131.1 - 156%) -- guaranteed OHKO
Wobbufet. Not quite benefical if you go for encore but manages to live every attack of diancie 3HKO.
Fire :
No actual checks on fire for mega diancie. With its raw power diancie can pretty much wreck any fire team with earth power and diamond storm.
Steel :
No need any calcs for this I assume, half of steel types are soft checks to diancie. Celesteela calcs above for flying type.
Ghost :
Nothing in ghost type can freely switch into diancie except for mimikyu. While being outspeed mimikyu cant do any damage to diancie aswell.
Water :
Defensive non mega swampert with couple spdef ivs can switch into diancie's any attack and proceed to kill with earthquake. ( 144 spd )
252 SpA Diancie-Mega Moonblast vs. 252 HP / 144 SpD Swampert: 169-201 (41.8 - 49.7%) -- guaranteed 3HKO after Leftovers recovery
Overall analyze : Dragon Ice Fighting Fire and Ghost doesnt have actual checks and counters for mega diancie. Whatever you throw in might end up dead. Some types doesnt have more than 1 check with no counters.
Due to dual typings, pokemons with steel typing have great chance of checking diancie in other types, such as psychic bug and fairy. Chansey and p2 in normal just walls it without any major worry ( Crit might kill those ) .
It gets completely walled by steel teams.
It doesnt kill more than 1 pokemon in a counter team situation, in grass / ground / water /steel matchups. Might be even used as a setup fodder if getting correct predictions.
Revenge killing :
It has a monstrous 110 speed stat, but anything above 80 speed with scarf is capable of revenge killing it, the types diancie neutrally beats might beat diancie teams back by any luck. There are way too many pokemons in every type being viable scarf / speed boosting users that will manage to kill mega diancie on it own.
My conclusion (again) : Diancie mega is indeed a strong pokemon, can be countered by only several types but it is possible to revenge kill it with pretty much every possible type. I think its current situation is 50-50% , couldnt decide if its broken to be in metagame or it will fit it very well.