Pokemon GOis finally getting some much needed changes related to Mega Evolutions and with it has come a new Special Research titled A Mega Moment.
Mega Evolutions were pretty controversial when they were added to the game, as many people saw them as forcing people to spend money to do enough Mega Raids to get Mega Energy for one-time use Mega Evolutions.

Thankfully, Niantic has listened to the fans after all this time and has finally changed course with some major changes that should make players very happy.
What Is New With Mega Evolutions InPokemon GO?
Niantic is implementing a number of changes related to Mega Evolutions, starting first and foremost with the fact that you no longer have to have Mega Energy to continually evolve your Pokemon. Instead, you will just have to have the Mega Energy the first time and then will have a cooldown before you may do it again without any cost. However, you can spend additional Mega Energy to reduce the time you have to wait for the cooldown.
In addition, Mega Evolution raids are also going to be made easier to where fewer people will be required to complete them, though we do not know to what degree of reduction in difficulty this will mean yet.

One very helpful addition is the ability to Mega Evolve Pokemon from the raid and battle prep screens, which was not possible at all before.
Lastly,Pokemon GOis introducing what are known as Mega Levels, which increase the more you Mega Evolve your Pokemon. This will lead to more bonuses being active while your Pokemon is Mega Evolved, including the following directly from the Pokemon GO blog:
A Mega Moment Special Research Tasks and Rewards
The A Mega Moment Special Research is one of the rare researches inPokemon GOwith a split path based on a choice between three options.
The key for this Special Research is to give you plenty of Mega Energy for a specific Kanto starter’s final evolution between Venusaur, Charizard, and Blastoise. As a result, you should check to see how much Mega Energy you have for each one prior and pick the one you are lacking Mega Energy in.
As you’re able to see, the entire Special Research is reliant on that choice of starter evolution at the conclusion of Step 1. You will have as long as you want to complete this Special Research, but make sure to take advantage so you can get a jump on the new Mega Evolution perks as soon as possible.