What are blue raid eggs in Pokémon Go?

gamepur.com:

For a limited time, blue raid eggs will appear in Pokémon Go. These happen during specific events in the game, and they won’t be around for too long. These typically occur during a Community Day event, but they might during other special events staged by Niantic. These raids work effectively the same as traditional ones but provide unique benefits. Here’s what you need to know about blue raid eggs in Pokémon Go.

A blue raid egg in Pokémon Go is considered a four-star raid. Four-star raids were one of the original difficulty tiers in the mobile game, but these, along with two-star raids, were merged into one-star and three-star raids. Now, Niantic uses these blue raid eggs as four-star eggs, and they spawn shortly after the conclusion of a Community Day event.

Related: The best moveset for Staraptor in Pokémon Go

The blue raid eggs will spawn the second form of the featured Pokémon. For example, on Starly’s Community Day, Staravia would generate from these eggs after the event ended. If you and other players defeated Staravia at the raid, Starly would begin appearing within 300 meters of that location for the next 30 minutes. This allows players to work together to try and capture more of the Community Day Pokémon, despite the event being over. These effects also make it more worthwhile to work towards evolving Starly into its final form, Staraptor and teach it the Community Move, Gust.

You will likely see blue raid eggs whenever you participate in a Community Day event. These might occur in other events, and these are valuable opportunities if you’re looking to receive the spawn of a particular Pokémon.