Washington [US]: According to The Verge, the Mega Evolution was introduced to the mainline 'Pokemon' series in Pokemon X and Y and continued in 'Sun' and 'Moon', but it doesn't appear in the most recent games 'Sword' and 'Shield', which have a similar feature called Dynamax.
In 'Pokemon Go', Mega Evolution is handled with a new resource called Mega Energy that is earned by battling Mega-Evolved pokemon in raids. The players can Mega Evolve Pokemon including Beedrill, Blastoise, Charizard, and Venusaur once they have enough energy.
The pokemon will become much stronger in their new forms, so Mega Evolution is likely to have major implications for high-level play.
As per the Verge, only one Mega-Evolved pokemon can be held at once, which is presumably a nod to the effect's temporary nature in the mainline series. A new Pokedex feature will let the gamer keep track of which pokemon the player Mega Evolved in the past. Once the player Mega Evolved a specific pokemon a single time, he-she won't need as much energy to do so again in the future.
(Inputs from ANI)