Mega Evolution is a new concept that has been introduced in the main series of games and brought over to this series with Pokémon Shuffle. To activate the Mega Evolution, you need to have captured the Pokémon which can Mega Evolve and obtain its Mega Stone from a trainer battle at the end of each world.
Once done, if that Pokémon is the lead in your party then as you make matches with it, a special Mega Gauge will fill up. This gauge will also fill up if you have a Pokémon of the same type with the ability of Mega Boost. When the Mega Gauge is filled, all instances of this Pokémon will Mega Evolve and gain a new ability. When you match the Pokémon, this ability will come into force and will always clear a portion of the board.
As of Version 1.2.0, each Mega Evolved Pokémon has got a special counter with a Rare Candy to boost the speed of Mega Evolution.
Currently Available Mega Evolutions
Mega Stone Location
Mega Power Erases 5 Pokémon in the columns to the left and right of the Pokémon in the chain 3