Giovanni has a new Shadow Pokémon in Pokémon Go. For a limited time, you will be able to rescue Shadow Lugia from Giovanni, as long as you complete the Season of Mischief Seasonal Special Research Mission, Misunderstood Mischief. The final tasks in this special research story see you take on Team Rocket and fight Giovanni. Once defeated, you will be able to capture Lugia. Should you purify Shadow Lugia or keep it as a Shadow Pokémon in Pokémon Go?
We can't stress enough that you should keep Lugia Shadow as a Shadow Pokémon. It's not every day that you face Giovanni and rescue a Legendary Shadow Pokémon. These encounters are extremely rare, even more so than fighting a Legendary Pokémon in a five-star raid and catching it. You can do this multiple times during an event, but Shadow Pokémon are typically limited to one encounter, with most players only getting one chance to catch one.
Due to this rarity, it is generally best to keep a Legendary Shadow Pokémon as a Shadow. We've recommended it in the past for other Legendary Pokémon that have also had shadows alongside Giovanni, even though their shadow version wasn't as good as the original. The rarity of these Pokémon far exceeds the potential for PvP or PvE battles. Thankfully, the shadow version of Lugia is essentially on par, if not better, than the other original.