IT'S RUMOR TIMEEEE!!!!!
Mega Mewtwo (Pure Forme). In addition to Mega Mewtwo, a second Mega Evolution of Mewtwo exists which is much smaller and friendlier looking, with its tail wrapping around its body. It is Psychic-type, and has "Magic Guard". It is said that Trainers who have proven themselves to have strong hearts may bear witness to this Forme that, while small, is rumored to possess extremely potent psychic powers.
Mega Magcargo. It becomes Fire-type as it breaks out of its shell, resembling a larger fiery snail with the back of its body bubbling up with heat bubbles. It gains a boost in Special Attack and has Flash Fire as an Ability. It is described as its body raising to excessive temperatures that prevent it body from cooling down whatsoever.
Mega Drifblim. It is Ghost/Flying, and its upper body swells to a larger size and it has six "arms" now instead of two, but mostly stays the same looking. The larger size gives it stronger Defense and Special Defense than before, and it has a new Ability, "Sky High", which prevents it from being grounded. It is described as its body swelling to massive sizes as it takes to the air to heights that most Pokemon are incapable of reaching.
Mega Jynx. It is Ice/Psychic, and its body slims down and it has a more "hotter" look to it, with its hair turning an icy silver. Its slimmer size gives it more Speed, and it also has stronger Special Attack, and has Cute Charm as an Ability as it has an alluring look to it. It is described as using its Psychic powers to create a strange illusion that gives it a beautiful look that no Pokemon can resist.