Revealed earlier today, there will be two versions of Mega Charizard, which will be split to be exclusive to either Pokemon X or Pokemon Y! We do have more information on what makes them unique, however. Just like how Mega Mewtwo X will be primarily focused on physical moves (Psychic/Fighting) and Mega Mewtwo Y will be primarily focused on special attack moves, Mega Charizard X will have a heavier emphasis on physical moves.
Mega Charizard X will be a Fire/Dragon type, gaining the ability Tough Claws during its Mega Evolution stage. Tough Claws drastically increases the damage output from physical moves, as well as being able to learn the move Dragon Tail.
Mega Charizard Y, however, will gain the ability Drought, which drastically increases the power of Fire-type moves. Additionally, while in its Mega Evolution stage, Mega Charizard Y’s special attack stat boosts passively, therefore intensifying its special attack-based moves. Mega Charizard Y will be able to learn the move Blast Burn, which, in combination with Drought and its passive bonus, makes for one slick burn!