Mega Evolutions have been in Pokemon GO for a while now and the game provides multiple ways of earning that coveted Mega Energy.
Mega Evolution was first introduced in the X and Y series. Pokemon could hold specific stones that allowed them to Mega Evolve during battle. That often increases their power and sometimes changes their typing.
In Pokemon GO, Mega Evolutions occur when a player has harvested enough Mega Energy. The temporary transformation lasts for a certain time period in-game. There is also a Mega Energy for each Pokemon's Mega Evolution. That means several different types will need to be obtained for each Pokemon.
How to get Mega Energy in Pokemon GO
Similar to Candy in Pokemon GO, Mega Energy is specific to each Pokemon. The easiest way to get a hold of Mega Energy is completing a Mega Raid. This is a Pokemon GO Raid where the trainer battles a Mega Evolved Pokemon.
Special Research rewards also give Mega Energy in certain situations. There have been several rewards that have delivered Mega Energy to the trainer and Pokemon. More than likely, there will be others in the future.
Players can also select Mega Evolution-capable Pokemon as their Buddies. This Pokemon GO feature allows the in-game character and the Pokemon to walk the world together. Each one has a certain distance to travel before a Candy is given.
In addition to Candy, Mega Evolution-capable Buddies will provide that sweet sweet Mega Energy after the proper travel distance has been reached. These are the most common ways to earn Mega Energy in Pokemon GO.
Niantic is always adding new things to the mobile game, however. Other ways to obtain Mega Energy could be revealed at any time. Also note that only one Pokemon can be Mega Evolved at any given moment. If a second Pokemon Mega Evolves while one currently is, the first one will revert to its normal form.