So, it doesn't looks like, but Aerodactyl-Mega is the perfect partner to Whimsicott and I'll explain the why. First of all, Aerodactyl-Mega sports cool Speed and Attack Stats, and this is pretty good for Whimsicott, since it has some troubles to defeat Fire-Types (Aerodactyl can OHKO all of them after SR, and it is faster than them). Whimsicott has some troubles to bulky Pokémon, like Florges, Defensive Sylveon and Blissey, but Aerodactyl can use one Hone Claws and 2HKO them. But Whimsicott's role is very good to Aerodactyl-Mega too, mostly because of it's ability to KO Water-Types and use Encore to stop Setup Sweepers and allow Aerodactyl to setup Hone Claws. Whimsicott is a good Pivot to stuff like Scarf Hydreigon, and it can just take advantage of it's typing to defeat Ground-Types too. Hopefully, Aerodactyl-Mega can learn Earthquake, what is a useful tool to defeat non-Shuca Cobalion, Doublade (in switch after +1) and Empoleon, but Steel-Types are still dangerous to this core. That's why I always run Pokémon like Entei and/or Tentacruel with this core.
Cobalion @ Life Orb
EVs: 252 SpA / 4 SpD / 252 Spe
IVs: 0 Atk
- Focus Blast
- Flash Cannon
- Stealth Rock
- Volt Switch
Cobalion makes an offensive volt/turn core with whimsicott. Whimsicott enjoys the residual damage from Stealth Rocks being on the field as well as cobalions Ability to deal with steels amd poison types that arnt nidoking/queen. Taking advantage of eachothers resistances and their decent speed teirs they can switch back and forth wearing down a large portion of the meta. I went with a special rocker cobalion because it has a bit of surprise factor and doesnt waste any evs using volt switch and is also a great reciver for nasty pass celebi if youre into that kinda thing ;)
Chandelure @ Leftovers
Ability: Flash Fire
EVs: 252 SpA / 4 SpD / 252 Spe
- Calm Mind
- Shadow Ball
Some of the more common Pokemon used to check offensive Whimsicott include specially bulky Pokemon like Blissey, Sylveon, and Florges, as well as Fire- and Poison-types like Entei, Arcanine, and Roserade. SubCM Chandelure takes full advantage of these Pokemon, setting up on them with ease and breaking them for Whimsicott to go to town. This is made even better considering that Whimsicott can give Chandelure even more setup opportunities via Encore + U-Turn. While it can't always set up on them, Chandelure can check Steel-type Pokemon that give Whimsicott trouble, like Mega Aggron, Forretress, and sometimes even Doublade (must be healthy enough to survive a Shadow Sneak). Finally, Whimsicott checks Pokemon that are annoying for Chandelure to face, such as Hydreigon, Krookodile, and bulky Water-types.
Darmanitan @ Choice Scarf
Ability: Sheer Force
EVs: 252 Atk / 90 SpD / 168 Spe
- Flare Blitz
- Rock Slide
Whimsicott's ability to remove bulky Water-Types and Ground-Types, without 'Nido' in their name, is appreciated by Darmanitan as they prevent it from cleaning late game/revenge killing. Earthquake coverage and Flare Blitz STAB on Darmanitan can check Whimsicott's Poison and Steel threats respectively. Together the two form an offensive U-Turn core that Whimsicott can use to bring Darmanitan in to Specially Defensive Pokemon that wall it, while Darmanitan can keep momentum early and mid game along with wearing down anything that switches into it. Effectively, the core looks to break down each other's checks to then allow a late game clean.
The EVs on Darmanitan still let it outspeed and revenge a weakened Mega Aero and Crobat with Scarf, who cause Whimsicott problems, and the added SpD let it survive a Sludge Wave/Bomb from the Nidos and Roserade in tight late-game spots. While Darmanitan's pitiful bulk and recoil can be a problem, the ability to pivot and revenge some of Whimsicott's biggest threats make it a good partner to the little pixie.
This core has a weakness to Entei and Mega Aggron, however another team member could help mitigate these threats such as Swampert, Suicune or Slowking (all of which form a nice FWG core)
What switches into Whimsicott that we might expect to be U-Turning into? Bronzong, Tentacruel, Empoleon, Forretress, Nidoqueen/king, Crobat, Doublade, Blissey. Nearly all of these are threatened hard by Krookodile. Twice as nasty is the fact that Pursuit and the threat of Pursuit can assure that you take out things like Bronzong, which not only opens the door for Whimsicott, but also a host of other possibilities like Crobat or Mega Aero. Tentacruel is a bit trickier because it is faster than Krook, but if Whimsicott has attacked Tentacruel at least once, it should be relatively easy to get a sense for how much HP/SpD Tentacruel is running and therefore how much Speed it has committed to outrunning Krookodile. Even nicer, the best switch-ins to Krookodile are Chesnaught and Tangrowth, and offensive Whimsicott switches very nicely into each of them.
Krookodile @ Choice Band
EVs: 4 HP / 252 Atk / 252 Spe
- Knock Off
SD Infernape has not been the most common set used in the meta, but with the recent bans of mence and kazam, it really gets to shine. A lot of Whims common checks and counters are obliterated by this set. The combination of fire fighting and ground is able to defeat mons such as blissey, chandelure, florges, sylveon, tentacruel and a lot more at +2. Whimsicott on the other hand weakens / defeats bulky waters and gives infernape plenty of set-up opportunities with encore+u-turn. It also defeats some common scarfers such as Hydreigon if not running mach punch. This core aims to have Whimsicott weaken Infernapes counters and find a opportunity for ape to set up and clean up, or have ape punch holes early game while having Whims generating momentum for another teammate to sweep. The last move slot on Infernape depends on the team itself. Earthquake allows ape to sweep easier, being able to hit mons such as chandelure, while mach punch allows Infernape to pick off weakened pokemon such as M-aero.
Mega Houndoom partners very well with Whimsicott due to their excellent offensive synergy. Whimsicott can switch into and beat Water, Ground and Fighting types that Houndoom can't power trough without a boost (Suicune, Swampert and Conkeldurr for example) and provides useful momentum on Steel switch-ins with U-Turn. Houndoom loves the opportunity of a free turn for set-up and Whimsicott can help create these situations thanks to its typing and U-Turn. Additionally, Whimsicott makes for a fine answer to Hydreigon, a top tier threat that resists both of Houndooms STABs. Other options like Stun Spore or Tailwind can improve Houndooms sweeping potential by slowing down/outspeeding fast threats like Mega Aerodactyl or Scarfers. On the other side, Houndoom can absorb opposing Fire type moves pre-mega thanks to Flash Fire and also beats Grass and Steel types like Roserade and Doublade for Whimsicott.
I think that I don't need to explain, but Sceptile-Mega can defeat Bulky Waters and can absorb Electric-Type attacks for Gyarados, while Gyra can defeat Steel-Types and resist Ice Shards from Mamoswine for Sceptile.
Nidoqueen @ Life Orb
Ability: Sheer Force
EVs: 40 HP / 252 SpA / 216 Spe
IVs: 0 Atk
- Stealth Rock / Toxic Spikes
- Sludge Wave
- Earth Power
- Thunderbolt / Focus Blast
Nidoqueen makes a great partner for DD Gyara for a number of reasons. It provides defensive synergy through an Electric immunity, bulky Grass-type (primarily Chesnaught) check, and Fairy check (primarily Sylveon). In return, Gyarados checks opposing Ground-types, such as Mamoswine and Mega Swampert, while also hindering opposing offensive Water-types through Intimidate + resisting Water.
Offensively, Nidoqueen supports a Gyarados sweep through laying hazards and luring some of Gyara's checks and counters. Stealth Rock is obviously beneficial, but if you can fit another user on your team then Toxic Spikes is great for wearing down common Gyara checks such as bulky Water-types, Porygon2, Umbreon, and Heliolisk. Nidoqueen can also lure some of Gyara's checks with its coverage move; Thunderbolt hits bulky Water-types, Mandibuzz, and opposing Gyarados, while Focus Blast hits Porygon2, Umbreon, and Hydreigon. Both options also blow past Shuca Empoleon.
Krookodile is a great partner for gyarados as it supports its sweep immensely. First of all, Krookodile is a electric immunity, being able to take on mons such as Mega Ampharos, which threatens a gyara sweep. Krookodile also provides rocks, which are extremely efficient to wearing down opposing threats with the combination of knock off. Krookodiles Knock Off cripples a lot of defensive checks to gyarados, stripping away eviolites of porygon, doing huge damage to cress, getting rid of leftovers from bulky waters etc... Krookodile is also able to check Mega-Aero, which can revenge gyara even at +1. The 2 also form a dual intimidate core which helps check physical threats while having defensive utility. While having dual intimidate, they also support great type synergy when dealing with each others checks. As mentioned before, krookodile is immune to electric, while also resisting rock. Gyara on the other hand can take fighting and bug type moves for krookodile and threaten some grass types with bounce.
Textbook Mamoswine is a great partner for gyara for many reasons: First of all its immune to gyaras main weakness and keeps electric types from clicking volt switch without thinking about it. In exchange gyara can take fighting type attacks for mamo and even switch in on fire types to some extent (especially if you have cleric on your team). On top of that it is able to weaken a lot of gyaras checks like P2, chesnaught or all of these pesky water/grass types which opens up a door for a sweep. Last but not least the icing on the cake: (Puns) priority ice shard which threatens faster pokemon or scarf users like m-aero or hydreigon and complements the synergy.
Bog-standard Offensive Whimsicott is a greater partner for SubDD Gyarados. Whimsicott handles most of the bulky Water-Types that can wall Gyarados or prevent it setting up (Roarcune specifically). Whimsicott also creates plenty of setup opportunities for Gyarados with it's Prankster priority-boosted Encore. Running Earthquake on Gyarados can handle the Poison Types that Whimsicott fears such as Tentacruel and the two Nidos. Given the oppourtunity to setup, Gyarados can also deal with the special walls that Whimsicott struggles against.
Overall these two mons partner well, covering each other's checks while keeping up offensive pressure. They also provide useful support for a team with Whimsicott being able to keep momentum with U-turn and Gyarados shutting down physical attackers with Intimidate.