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What are Purified Gems and how do I collect them?
Purified Gems are special Items that can be used in a Shadow Raid to help defeat the Shadow Raid Boss.
In order to create a Purified Gem, you must collect Shadow Shards by defeating Team GO Rocket Grunts, Leaders, and Giovanni in Pokémon Battles. They will drop Shadow Gem Pieces as part of your rewards for defeating them. Collect 4 Shadow Shards and use the Shard Refiner to create a Purified Gem. You can hold up to 10 Purified Gems at a time.
Once you have formed a Purified Gem, you can use it in a Shadow Raid Battle, when the Raid Boss is enraged. Purified Gems can subdue the Shadow Raid Boss, neutralizing their enraged state and making them easier to defeat.
This effect will stack if other Trainers in the Shadow Raid Battle also use Purified Gems. Each Trainer can use up to 5 Purified Gems in a Shadow Raid Battle.
Source: Official Pokémon GO support page
What are Shadow Raids?
A Shadow Raid is a mysterious type of Raid Battle that occurs at a Gym that has been taken over by Team GO Rocket.
Unlike a standard Raid, a member of Team GO Rocket has captured the Gym and placed a Shadow Pokémon as the Raid Boss. Enter the Gym and defeat the Shadow Raid Boss in battle to get the chance to capture it. Like a standard Raid, Shadow Raids have multiple difficulty levels depending on the strength of the Shadow Raid Boss.
Once a Gym has been taken over by Team GO Rocket, the Raid Egg above the Gym will appear with a purple flame behind it. Once the Raid Egg has hatched, the Gym will change color to appear black on the Map. Shadow Raids are also visible on your Nearby menu; the Raid Boss or Raid Egg will feature a purple flame behind it.
As you approach the Gym, Team GO Rocket Grunts, Leaders or Giovanni will appear nearby if you are in range. Tap the Gym to enter the Raid Battle using a Raid Pass. Note that Remote Raid Passes are not eligible to be used in Shadow Raids.
At a certain point during the Raid Battle, the Shadow Pokémon may become enraged, which will make it more difficult to defeat.
If you have a Purified Gem in your bag, a button will appear on the bottom left of your screen after the Shadow Pokemon has become enraged. Tap the button to use a Purified Gem, which will help to subdue the Shadow Raid Boss and return it to its non-Enraged state. Learn more about Purified Gems.
If you and your fellow Trainers are successful in defeating the Shadow Raid Boss, you’ll earn special items and a chance at catching the Pokémon. Just like in a standard Raid Battle, you will receive Premier Balls as one reward for your performance in the Raid Battle. Use the Premier Balls to try and catch the Shadow Pokémon.
Source: Official Pokémon GO support page
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