Mega Evolution (Charizard)
Mega Charizard X (メガリザードンX, Mega Lizardon X) is the Mega Evolution of Charizard in the Pokémon games using a Mega Stone that is exclusive to Pokémon X. It appears in Super Smash Bros. 4. It is currently unknown how the Mega Evolution is activated, nor how much stronger Charizard gets when in this form.
Origin
Mega Evolution is a mechanic introduced in Pokémon X and Y. Only a small amount of Pokémon—including Charizard—can Mega Evolve, and to do so it must hold a special Mega Stone unique to its species. A Pokémon can Mega Evolve in battle, but a trainer can only use one Mega Evolution per battle. The Mega Evolution can change some of the following to the Pokémon itself such as stronger stats (a few Mega Evolutions sometimes decrease stats in favor for others), a different typing, and a different ability. Charizard can Mega Evolve by holding onto a Charizardite X or a Charizardite Y as its item. Charizard is one of two Pokémon (the other being Mewtwo) that have two Mega Evolution forms, the two forms being an "X" form and a "Y" form, with the particular Mega Stone only appearing in Pokémon X and Pokémon Y respectively.
Gallery
Mega Charizard X flying in Super Smash Bros. for Wii U.
Close up of Mega Charizard X in Super Smash Bros. for Wii U.