Mega Evolution in Pokémon X & Y

Pokémon X & Y introduced a new type of evolution called Mega Evolution. When holding a particular Mega Stone (specific to each Pokémon), certain Pokémon can Mega-Evolve in battle.

Mega Evolution is in fact more like in-battle form changes. Mega Pokémon do not occupy separate spots in the Pokédexes.

Mega Venusaur
#003
Mega Venusaur
Grass · Poison
Mega Charizard X
#006
Mega Charizard X
Fire · Dragon
Mega Charizard Y
#006
Mega Charizard Y
Fire · Flying
Mega Blastoise
#009
Mega Blastoise
Water
Mega Alakazam
#065
Mega Alakazam
Psychic
Mega Gengar
#094
Mega Gengar
Ghost · Poison
Mega Kangaskhan
#115
Mega Kangaskhan
Normal
Mega Pinsir
#127
Mega Pinsir
Bug · Flying
Mega Gyarados
#130
Mega Gyarados
Water · Dark
Mega Aerodactyl
#142
Mega Aerodactyl
Rock · Flying
Mega Mewtwo X
#150
Mega Mewtwo X
Psychic · Fighting
Mega Mewtwo Y
#150
Mega Mewtwo Y
Psychic
Mega Ampharos
#181
Mega Ampharos
Electric · Dragon
Mega Scizor
#212
Mega Scizor
Bug · Steel
Mega Heracross
#214
Mega Heracross
Bug · Fighting
Mega Houndoom
#229
Mega Houndoom
Dark · Fire
Mega Tyranitar
#248
Mega Tyranitar
Rock · Dark
Mega Blaziken
#257
Mega Blaziken
Fire · Fighting
Mega Gardevoir
#282
Mega Gardevoir
Psychic · Fairy
Mega Mawile
#303
Mega Mawile
Steel · Fairy
Mega Aggron
#306
Mega Aggron
Steel
Mega Medicham
#308
Mega Medicham
Fighting · Psychic
Mega Manectric
#310
Mega Manectric
Electric
Mega Banette
#354
Mega Banette
Ghost
Mega Absol
#359
Mega Absol
Dark
Mega Garchomp
#445
Mega Garchomp
Dragon · Ground
Mega Lucario
#448
Mega Lucario
Fighting · Steel
Mega Abomasnow
#460
Mega Abomasnow
Grass · Ice