The first Mega to be revealed this month is a Mega Gallade. Mega Gardevoir was introduced in Pokémon X and Pokémon Y, so it seems fitting that Wally would find himself with a Mega Gallade. Nothing about the Mega Evolution is currently known.
Next up we have a Mega Sharpedo which has the ability Strong Jaw when Sharpedo Mega Evolves. Apparently all of the Pokémon's stats are boosted when it Mega Evolves.
Lastly we have a Mega Camerupt. When Mega Evolved the Pokémon gets a drop in its Speed stat but everything else has been increased. Its ability becomes Sheer Force.
CoroCoro has also revealed that Primal Kyogre and Primal Groudon will have new abilities. Primal Groudon gets the new ability Land of Endings which will activate Strong Sunlight, while Primal Kyogre has the ability Sea of Beginnings which activates Strong Rain. Groudon is also confirmed to know a new move known as Cliff's Blade.
The magazine is still leaking so more information may yet be revealed, so keep checking back!