Seperti dalam ulasan sepintas Pokemon X dan Y sebelumnya, disebutkan bahwa dalam game generasi VI tersebut ditambahkan sistem Mega Evolution. Selaku developer GameFreak, memaparkan tidak semua, hanya beberapa Pokemon saja yang dapat melakukan Mega Evolution. Dengan Mega Evolution memungkinkan Pokemon berubah menjadi bentuk Mega yang lebih kuat dalam sebuah battle, dengan menggunakan key item Mega Ring dan Mega Stone yang sesuai. Begitu setelah battle berakhir Pokemon tersebut akan kembali ke bentuk awalnya. Berikut ini daftar Mega Evolution dalam game Pokemon X dan Y disertai dengan stats.
Mega Charizard X
Type: Fire-Dragon
Ability: Tough Claws
Base Stats: HP 78, Attack 130, Defense 111, Special Attack 130, Special Defense 85, Speed 100
Mega Stone: Charizardite X
Mega Charizard Y
Type: Fire-Flying
Ability: Drought
Base Stats: HP 78, Attack 104, Defense 78, Special Attack 159, Special Defense 115, Speed 100
Mega Stone: Charizardite Y
Mega Venusaur
Type: Grass-Poison
Ability: Thick Fat
Base Stats: HP 80, Attack 100, Defense 123, Special Attack 122, Special Defense 120, Speed 80
Mega Stone: Venusaurite
Mega Blastoise
Type: Water
Ability: Mega Launcher
Base Stats: HP 79, Attack 103, Defense 120, Special Attack 135, Special Defense 115, Speed 78
Mega Stone: Blastoisinite
Mega Mewtwo X
Type: Psychic-Fighting
Ability: Steadfast
Base Stats: HP 106, Attack 190, Defense 100, Special Attack 154, Special Defense 100, Speed 130
Mega Stone: Mewtwonite X
Mega Mewtwo Y
Type: Psychic
Ability: Insomnia
Base Stats: HP 106, Attack 150, Defense 70, Special Attack 194, Special Defense 120, Speed 140
Mega Stone: Mewtwonite Y
Mega Abomasnow
Type: Grass-Ice
Ability: Snow Warning
Base Stats: HP 90, Attack 132, Defense 105, Special Attack 132, Special Defense 105, Speed 30
Mega Stone: Abomasite
Mega Absol
Type: Dark
Ability: Magic Bounce
Base Stats: HP 65, Attack 150, Defense 60, Special Attack 115, Special Defense 60, Speed 115
Mega Stone: Absolite
Mega Aerodactyl
Type: Rock-Flying
Ability: Tough Claws
Base Stats: HP 80, Attack 135, Defense 85, Special Attack 70, Special Defense 95, Speed 150
Mega Stone: Aerodactylite
Mega Aggron
Type: Steel
Ability: Filter
Base Stats: HP 70, Attack 140, Defense 230, Special Attack 60, Special Defense 80, Speed 50
Mega Stone: Aggronite
Mega Alakazam
Type: Psychic
Ability: Trace
Base Stats: HP 55, Attack 50, Defense 65, Special Attack 175, Special Defense 95, Speed 150
Mega Stone: Alakazite
Mega Ampharos
Type: Electric-Dragon
Ability: Mold Breaker
Base Stats: HP 90, Attack 95, Defense 105, Special Attack 165, Special Defense 110, Speed 45
Mega Stone: Ampharosite
Mega Banette
Type: Ghost
Ability: Prankster
Base Stats: HP 64, Attack 165, Defense 75, Special Attack 93, Special Defense 83, Speed 75
Mega Stone: Banettite
Mega Blaziken
Type: Fire-Fighting
Ability: Speed Boost
Base Stats: HP 80, Attack 160, Defense 80, Special Attack 130, Special Defense 80, Speed 100
Mega Stone: Blazikenite
Mega Garchomp
Type: Dragon-Ground
Ability: Sand Force
Base Stats: HP 108, Attack 170, Defense 115, Special Attack 120, Special Defense 95, Speed 92
Mega Stone: Garchompite
Mega Gardevoir
Type: Psychic-Fairy
Ability: Pixilate
Base Stats: HP 68, Attack 85, Defense 65, Special Attack 165, Special Defense 135, Speed 100
Mega Stone: Gardevoirite
Mega Gengar
Type: Ghost-Poison
Ability: Shadow Tag
Base Stats: HP 60, Attack 65, Defense 80, Special Attack 170, Special Defense 95, Speed 130
Mega Stone: Gengarite
Mega Gyarados
Type: Water-Dark
Ability: Mold Breaker
Base Stats: HP 95, Attack 155, Defense 109, Special Attack 70, Special Defense 130, Speed 81
Mega Stone: Gyaradosite
Mega Heracross
Type: Bug-Fighting
Ability: Skill Link
Base Stats: HP 80, Attack 185, Defense 115, Special Attack 40, Special Defense 105, Speed 75
Mega Stone: Heracronite
Mega Houndoom
Type: Dark-Fire
Ability: Solar Power
Base Stats: HP 75, Attack 90, Defense 90, Special Attack 140, Special Defense 90, Speed 115
Mega Stone: Houndoominite
Mega Kangaskhan
Type: Normal
Ability: Parental Bond
Base Stats: HP 105, Attack 125, Defense 100, Special Attack 60, Special Defense 100, Speed 100
Mega Stone: Kangaskhanite
Mega Lucario
Type: Fighting-Steel
Ability: Adaptability
Base Stats: HP 70, Attack 145, Defense 88, Special Attack 140, Special Defense 70, Speed 112
Mega Stone: Lucarionite
Mega Manectric
Type: Electric
Ability: Intimidate
Base Stats: HP 70, Attack, 75, Defense 80, Special Attack 135, Special Defense 80, Speed 135
Mega Stone: Manectite
Mega Mawile
Type: Steel-Fairy
Ability: Huge Power
Base Stats: HP 50, Attack 105, Defense 125, Special Attack 55, Special Defense 95, Speed 50
Mega Stone: Mawilite
Mega Medicham
Type: Fighting-Psychic
Ability: Pure Power
Base Stats: HP 60, Attack 100, Defense 85, Special Attack 80, Special Defense 85, Speed 100
Mega Stone: Medichamite
Mega Pinsir
Type: Bug-Flying
Ability: Aerilate
Base Stats: HP 65, Attack 155, Defense 120, Special Attack 65, Special Defense 90, Speed 105
Mega Stone: Pinsirite
Mega Scizor
Type: Bug-Steel
Ability: Technician
Base Stats: HP 70, Attack 150, Defense 140, Special Attack 65, Special Defense 100, Speed 75
Mega Stone: Scizorite
Mega Tyranitar
Type: Rock-Dark
Ability: Sand Stream
Base Stats: HP 100, Attack 164, Defense 150, Special Attack 95, Special Defense 120, Speed 71
Mega Stone: Tyranitarite
Sejauh ini dalam seri game pertama untuk 3DS, hanya Mewtwo yang termasuk sebagai Legendary Pokemon yang memiliki akses Mega Evolution (dua sekaligus) pada Pokemon X dan Y. Charizard juga mendapat perlakuan khusus dengan memiliki dua Mega Evolution untuk Pokemon yang tidak termasuk Legendary. Aggron dengan type Steel-Rock, menjadi Mega Aggron yang mengubahnya menjadi murni type Steel. Catatan lain adalah Ampharos yang memiliki type Electric menjadi Mega Ampharos dengan type Electric-Dragon. Kangaskhan yang menjadi Mega Kangaskhan merupakan satu-satunya Pokemon type Normal dengan Mega Evolution dalam seri ini. Charizard, Venusaur, Blastoise, dan Blaziken adalah empat starter dengan Mega Evolution.
Lihat juga mengenai lokasi dari Mega Stone dalam Pokemon X Y.