Mega Evolutions

A brand new feature of the Pokémon X & Y games are Mega Evolutions. These are special features of Pokémon, different to evolutions and forms, that have your Pokémon Mega Evolve in battle into these appearances. Their abilities, stats and sometimes even types are different. The true method is not yet known, but Mega Stones have been mentioned.

MegaMewtwo

US Name: MegaMewtwo
Jp. Name: MegaMewtwo

Type: Psychic
Classification: Genetic Pokémon
Height: 1.5m
Weight: 33.0kg
Ability: Insomnia

First Appearance: Extremespeed Genesect: Mewtwo Awakens

Details:
This Pokémon was first leaked in a promotional pamphlet of the Present Guide for the movie Extremespeed Genesect: Mewtwo Awakens, replacing Mewtwo on the poster with a caption calling it the Eclair Forme. However, soon afterwards it was revealed by Pokémon Smash, though without saying it is actually a Mewtwo form with the official sites stating it as a new Pokémon.
It was eventually confirmed as a Mega Evolution in CoroCoro in August 2013
MegaBlaziken

US Name: MegaBlaziken
Jp. Name: MegaBashamo

Type: Fire/Fighting
Classification: Blaze Pokémon
Height: 1.9m
Weight: 52.0kg
Ability: Speed Boost

First Appearance: Pokémon X & Y

Details:
This Mega Evolution was first shown in August 2013's issue of CoroCoro. It features the special ability of Speed Boost
MegaLucario

US Name: MegaLucario
Jp. Name: MegaLucario

Type: Fighting/Steel
Classification: Aura Pokémon
Height: 1.2m
Weight: 54.0kg
Ability: Adaptability

First Appearance: Pokémon X & Y

Details:
This Mega Evolution was first shown in August 2013's issue of CoroCoro. It features the special ability of Adaptability
MegaMawile

US Name: MegaMawile
Jp. Name: MegaKucheat

Type: Steel/Fairy
Classification: Deceiver Pokémon
Height: 0.6m
Weight: 11.5kg
Ability: Huge Power

First Appearance: Pokémon X & Y

Details:
This Mega Evolution was first shown in August 2013's issue of CoroCoro. It features the special ability of Huge Power
MegaAbsol

US Name: MegaAbsol
Jp. Name: MegaAbsol

Type: Dark
Classification: Disaster Pokémon
Height: 1.2m
Weight: 49.0kg
Ability: Magic Bounce

First Appearance: Pokémon X & Y

Details:
This Mega Evolution was first shown in August 2013's issue of CoroCoro. It features the special ability of Magic Bounce
MegaAmpharos

US Name: MegaAmpharos
Jp. Name: MegaAmpharos

Type: Electric/Dragon
Classification: Light Pokémon
Height: 1.4m
Weight: 61.5kg
Ability: Mold Breaker

First Appearance: Pokémon X & Y

Details:
This Mega Evolution was first shown in August 2013's issue of CoroCoro. It features the special ability of Magic Bounce and features a change in type to Electric/Dragon