Friends

Friendship is a gameplay feature in Pokémon GO, which allows Trainers for wider range of cooperation within a game, including gifting and trading.

Details
Once a Trainer shares their Trainer Code with someone, that person can then send them a Friend Request. Friends can be made regardless of Teams. After two Trainers have become friends, they'll be able to send each other Gifts. Gifts are initially obtained by spinning the Photo Disc at a PokéStop or Gym.

Friends list
The Friends list is a contains a Trainer's friends. Each Trainer can have up to 200 friends. The list is sorted in order of friendship level and friends who sent you a Gift recently will appear at the top. The rest of your friends will be sorted by friends you have known the longest. There is no way to sort the list manually and you cannot favorite friends. There is also no way to contact them via messages, so you must have some other channel of communication if necessary.

Friendship levels
Friends will be able to help each other directly in Gyms and Raid Battles by activating bonuses. Great Friends will receive not only an Attack bonus to help them take down a Raid Boss at a much faster rate, but also extra Premier Balls to catch the Pokémon when the battle is complete. This adds more rewards and incentives for actions they’re already taking and can be especially beneficial for smaller groups of Trainers that battle together. When tight-knit friends take on a Raid Boss, even a small group can be mighty.

Once two Trainers become friends, they may trade all Pokémon (except Mythical) and send gifts to each other.

Gifting
When receiving a Gift from a friend, Trainers will see a postcard from the PokéStop or Gym where the friend acquired the Gift. Trainers are rewarded with 200 XP for sending Gifts.

Lucky Friends
When a Trainer becomes Lucky Friends with someone, the next time they trade with each other, both Pokémon will become Lucky Pokémon.

To become Lucky Friends, both Trainers must be Best Friends. Both Trainers will have a chance once per day when they trade Pokémon, open a Gift from each other, team up in raids and Gym battles, or challenge each other to a Trainer Battle. Both Trainers will receive a notification when they have become Lucky Friends and will be able to see that they are Lucky Friends in their Friend List and on their friend's profile page.

After completing the trade, the Lucky Friend status will return to Best Friend status. This can be accomplished again in the future.