Mega Evolution is a temporary power-up in Pokémon GO that increases a Pokémon's CP, gives it a new and more powerful form, and boosts other trainers' attacks in raids. Pokémon remain in their Mega forms for only four hours after they are Mega Evolved, and the first time this is done costs a great deal of Mega Energy, which can primarily be accrued from Mega Raids. After the first time, the cost is cut by 75%, but considering Pokémon such as Charizard and Blastoise have a cost of 200 Mega Energy, even the discounted future Evolutions aren't cheap. Because of these limitations on Megas, it is advisable to be picky and understand what trainers are getting into before they use this costly power-up. Using this guide, Pokémon GO trainers can determine when to Mega Evolve their Pokémon.
1. Your Pokémon will be useful in a raiding event
Instead of rushing to complete your Mega Dex, a strategic time to Mega Evolve your Pokémon would be if there is a raiding event where your it will be useful. A Cresselia Raid Hour, for example, would be a terrific time to Mega Evolve Beedrill. Beedrill, in its Mega Form, is one of the top Cresselia counters and will boost all other Bug-type Pokémon, which Cresselia, as a Psychic-type, is weak to. These sort of events, where you know you'll be raiding against a Pokémon weak to your Mega for an extended period of time, is the most recommended time to Mega Evolve. You can follow our raid guides to see if your potential Mega Pokémon is worth evolving for upcoming raid events.
2. Team GO Rocket takeover
These generally last a few hours and are battle-intensive. Even though, as these aren't raids, you won't be boosting any trainers, it would be smart to Mega Evolve for these so you can blast through more Team GO Rocket grunts and leaders at a quicker time.
3. You're going to spend four hours playing Pokémon GO
It's not all about strategy. It's a game, after all, so it's perfectly understandable to just get out there and have fun. There are plenty of things to do with your Mega Evolved Pokémon: walk with it as your Buddy, take GO Snapshot AR+ photos, and challenge friends to PVP battles. (By invite only: Megas aren't currently allowed in the GO Battle League.) Just make sure that you know you'll be playing the full four-hour stretch so you can truly optimize the time spent with your Mega Evolved Pokémon before it reverts back.