Like many new Pokémon games since the introduction of forms, Pokémon X & Y continues to add new forms to the fold. In addition to that, it provides .

New Pokémon Forms

#666 Vivillon

US Name: Vivillon
Jp. Name: Vivillon (ビビヨン)

Type: Bug/Flying
Classification: Scale Pokémon
Height: 3'11"
Weight: 37.5lbs

Vivillon's Form differences are unique in that you cannot change them or even natively get the different forms in your game. Instead, you get the version based on your geographic location set on the Nintendo 3DS, and is set when the Pokémon is caught or hatched. We're still in the process of collating which area gets which Pokémon

Meadow PatternPolar PatternTundra PatternContinental PatternGarden PatternElegant Pattern
Icy Snow PatternModern PatternMarine PatternArchipelago PatternHigh Plains PatternSandstorm Pattern
River PatternMonsoon PatternSavanna PatternSun PatternOcean PatternJungle Pattern
Vivillon's form is aesthetic and is dependant upon the geographic location set on your 3DS
#669 Flabébé, #670 Floette, #671 Florges

US Name: Flabébé
Jp. Name: Furabebe (フラベベ)

Type: Fairy
Classification: ?? Pokémon
Height: 0'04"/0.1m
Weight: 0.1kg
Ability: Flower Veil

Flabébé's form change is something merely aesthetic rather than a functional form. In Pokémon X & Y, you will find and capture numerous Flabébé, each with different coloured flowers depending upon the location. These forms are not interchangeable and do not have an effect on the stats of the Pokémon. This form then carries on through its evolution so if you have a red Flabébé and evolve it, you will get a red Florges

Red Flower Blue Flower Orange Flower White Flower Yellow Flower
Red Flower Blue Flower Orange Flower White Flower Yellow Flower
Red Flower Blue Flower Orange Flower White Flower Yellow Flower
Red Flower Blue Flower Orange Flower White Flower Yellow Flower
#676 Furfrou

US Name: Furfrou
Jp. Name: Torimian (トリミアン)

Type: Normal
Classification: Poodle Pokémon
Height: 3'11"
Weight: 61.7lbs
Ability: Fur Coat

Furfrou is another aesthetic form change, however it is one which you have complete control over. When you have a Furfrou, you will be able to groom it. Periodically, you'll be informed that Furfrou needs grooming and you can choose to do it. If you ignore its grooming regime, its hair will grow back to the size of it when it is captured. This is done at Frieser Furfrou in Vernal Avenue in Lumiose City and costs 500P per trim.

Natural FormHeart TrimStar TrimDiamond TrimDeputante Trim
Matron TrimDandy TrimLa Reine TrimKabuki TrimPharaoh Trim
#681 Aegislash

US Name: Aegislash
Jp. Name: ?? ??

Type: Steel/Ghost
Classification: Royal Sword Pokémon
Height: 5'07"
Weight: 116.8lbs
Ability: Stance Change

Aegislash's forms are the first set of forms to actually showcase the concept in Kalos. This Pokémon will change its form depending upon what moves it makes. The Formes are unique in that they completely swap their base stats with a focus on Attack in Blade Forme and Defence in Shield Forme If it makes any attacking moves, it switches to Blade Forme, whereas if uses the move King's Shield, it will be in its Shield Forme. Whenever it is sent out into battle, it is in its Shield Forme allowing for switching in without damage.

Shield Forme Blade Forme
Shield Forme Blade Forme
#710 Pumpkaboo & #711 Gourgeist

These two Pokémon also have got a unique form difference. However, unlike other form changes, these forms cannot be changed after capture. When you encounter the Pumpkaboo in the wilrd, it will be one of four possible sizes: Small, Average, Large and Super Size, with Super Size being the rarest. The difference is actually in their stats. While as a Pumpkaboo, its Hit Points go up, the larger it is, but the Speed decreases wheres when it has been traded to evolve into a Gourgeist, its Attack stat also starts getting larger for the larger forms while Speed decreases.

Small Size Average Size Large Size Super Size
Small Size Average Size Large Size Super Size
Small Size Average Size Large Size Super Size

Classic Pokémon Forms

#479 Rotom

Changeable?: Yes

Rotom's five alternate forms make a return within this game. When you have sent Rotom over, you will be able to take Rotom with you to the 2F of Professor Sycamore's Lab. In this store, there is a room with multiple storage boxes. Interact with this box and you'll be able to change your Rotom's form. These Rotom all have special attacks that can only be used while in that form and they change type

Rotom Mow Frost Heat Fan Wash
Rotom Mow Rotom Frost Rotom Heat Rotom Fan Rotom Wash Rotom
  Leaf Storm Blizzard Overheat Air Slash Hydro Pump
Base Stats:

HP: 50
Attack: 50
Defense: 77
Sp. Attack: 95
Sp. Defense: 77
Speed: 91
Base Stats:

HP: 50
Attack: 65
Defense: 107
Sp. Attack: 105
Sp. Defense: 107
Speed: 86