So, there are some people who approached me with this statement: "I'm gonna save up candy in Pokemon GO to mega evolve Eevee."
Okay... So Eevee can evolve now? NO! Not all Pokemon can mega evolve.
Since mega evolution in Pokemon is new, so I would take this opportunity to breakdown every Pokemon from Generation 1 to Generation 7 which can mega evolve.
Mega Evolution
Mega Evolution is a temporary transformation affecting certain Pokemon that was introduced in Generation 6. Mega-Evolved Pokemon are identified by having "Mega" in front of their name.
There are 46 species of Pokemon that are capable of Mega Evolution, and there are 48 different Mega Evolutions.
Mega Evolution Introduced in X and Y
Mega Evolution Introduced in Omega Ruby and Alpha Sapphire
In the main series, the first Mega Evolution was featured in Mewtwo - Prologue to Awakening, where Mewtwo was shown to be capable of changing between its regular form and Mega Mewtwo Y form, in which its speed was dramatically boosted, being capable of moving faster than the blink of an eye.
The same Mewtwo also played a major role in the movie, Pokemon - Genesect and the Legend Awakened which premiered in 2013, once again demonstrating its Mega Evolution capabilities. Unlike in the game, this Mewtwo seemed to be capable of Mega Evolving without the use of a Mega Stone. However, upon its original appearance, the concept of Mega Evolution had not yet been revealed, so the form did not yet have a name.
Now, the first Mega Evolution is officially introduced in the Generation 6, Pokemon X and Y - Kalos, Where Dreams and Adventures Begin!, where Ash saw a Mega Blaziken. It was revealed to belong to a masked hero called the Blaziken Mask, which is then unmasked in the later of the series to be Clemont and Bonnie's father. Mega Blaziken has since been seen helping Ash and his friends on numerous occasions.
In Mega Evolution Special I, a Trainer named Alain was featured traveling across the Kalos region with his Mega Charizard X, challenging other Mega Evolution Trainers. During the episode, Alain battled Astrid's Mega Absol and Remo's Mega Garchomp, and was victorious in both battles. Later in the special, he even faced the Elite Four member Siebold and his Mega Blastoise, but the powerful Water-type Pokémon proved to be too much for Charizard, causing Alain to lose the battle.
Professor Sycamore theorizes that Mega Evolution can only be achieved if there is a strong bond between a Trainer and its Pokemon. Of course, it also requires a Key Stone and an appropriate Mega Stone to Mega Evolve. Only Rayquaza does not need a Mega Stone to Mega Evolve, instead it must know the move Dragon Ascent.
But in the series Pokemon: X and Y and Pokemon: XYZ, Ash's Greninja does not need a Key Stone or Mega Stone to Mega Involve. It shows that how strong the bond between Greninja and Ash allow it to Mega Evolve into Mega Greninja. Well, this is a special case since Greninja is not capable of Mega Evolve.
So let me know in the comment on your opinion on Mega Evolution. Or you can also visit our Pokemon page.