ORAS - Mega Charizard Y or Shiny Pikachu

[Mega Sceptile]

From Serebii:

Pokémon Omega Ruby & Alpha Sapphire - Japanese Charizard Event

A new event has been announced. To commemorate the new Pokémon Center in Tokyo, two Pokémon are set to be distributed. From December 12th to January 16th, at the Pokémon Center in Tokyo, you can download either a shiny Charizard holding the Charizardite Y or a shiny Pikachu. The distribution is given based on the hour of the day, with them alternating. Details of the event Pokémon are not yet known but the Event Database has been updated with these events

[SnorlaxMonster]

Actually, the Pokemon will be available at all Pokemon Center stores, not just the Tokyo store.

全国8店舗のポケモンセンターでプレゼントするから、近くのお店へ行こう!!

Source: http://www.pokemon.co.jp/ex/pokecen_megatokyo/present/

Also, it will be available on December 11 at the Pokemon Center Mega Tokyo launch party.

Source: this magazine page

[ignisrothe]

Pokemon: Charizard (Shiny)

Gender: Male

Level: 36

OT: メガトウキョ

ID: 12124

Ability: Blaze

Nature: Random

Moves:

Overheat

Solar Beam

Focus Blast

Hold Hands

Item: Charizardite Y

Pokeball: Cherish

Ribbon: Premier

Location: a Pokemon Center

Dates: December 12, 2014 - January 16, 2015

Game Distribution: XY, ORAS

Distribution Type: Local Wireless

Distribution Location: Pokemon Centers

Pokemon: Pikachu (Shiny)

Gender: Random

Level: 36

OT: メガトウキョ

ID: 1214

Ability: Lightning Rod

Nature: Random

Moves:

Thunder

Substitute

Play Nice

Hold Hands

Item: None

Pokeball: Cherish

Ribbon: Premier

Location: a Pokemon Center

Dates: December 12, 2014 - January 16, 2015

Game Distribution: XY, ORAS

Distribution Type: Local Wireless

Distribution Location: Pokemon Centers

Sources: Official website