Unfortunately, not all of the Pokémon are readily available for capturing, though, depending on what events are happening in the game. So, you'll have to strike when the Pokémon you're looking for are there.
Mega Raids are one way to get certain Pokémon — but what is a Mega Raid? Let's break it down.
What is a Mega Raid?
Mega Raids function similarly to any other raid in Pokémon GO. Different gyms in your area will hatch a Raid Egg at a certain time, hosting a particular Pokémon at that gym for players to defeat for a chance to capture.
There are four tiers to all raids in the game: Tier 1, Tier 3, Tier 5, and Mega Raids. While Tier 5 Raids are often considered to be incredibly difficult, Mega Raids are usually even harder, requiring more powerful Pokémon when going into them.
In these raids, you'll battle against the Mega Evolutions of certain Pokémon, depending on what Raid Bosses are available that month. While you'll only be able to catch the regular version of that Pokémon, you'll earn Mega Energy during the battle.
There are also Legendary Mega Raids, which feature the Mega Evolutions of Legendary Pokémon. Understandably, these are the most difficult raids to tackle in the game.
Here's how to join a Mega Raid in 'Pokémon GO.'
Thankfully, joining a Mega Raid is just as easy as it is to join any other raid in Pokémon GO. You'll have to find a gym that's hosting a Mega Raid near you and make sure you're within proximity of it when the raid is happening. You can check your "Nearby" tab to locate the closest Mega Raid, indicated by the mega icon.
When the raid has started, you can join the Mega Raid with your daily Raid Pass (or with a Premium Raid Pass if you've already used your free one for the day).
As the Pokémon found in Mega Raids tend to be incredibly powerful, it's best to go into the raid with a few other friends if possible to ensure that your Pokémon can take down the Raid Boss within the allotted amount of time.
Remember, the faster you defeat the Raid Boss, the more Mega Energy you'll get, which you'll want for your own Mega Evolutions. If you have more players with you when you take on the boss, you'll likely walk away with more Mega Energy.
Make sure you've studied the type match ups of the Pokémon you're facing off against in the Mega Raid. Type matchups will be very important to take down the Raid Boss in a quick and easy fashion. If you don't have any friends who are local to tackle the raid with you, see if there are any who will use Remote Raid Passes and invite them remotely.