Rare Candy is a special type of Pokémon Candy that can be fed to any Pokémon species in Pokémon Go. It substitutes any other Pokémon Candy, meaning that feeding Rare Candy to Pikachu will make the game treat it as Pikachu Candy. Rare Candy is one of the few possible Raid Rewards, and it was introduced to help Trainers power-up and evolve Pokémon they see very rarely, such as Porygon and Lapras. In Pokémon Go, rare candy and rare candy XL are both useable materials that you can give your Pokémon, increasing the amount of the specific candy they have. This allows you to power them up and improve their CP even further without having to catch more of the Pokémon or walking with them as your buddy to earn more of their candy.
Rare Candy is obtained by completing certain in-game tasks such as winning Raid Battles, completing Field Research tasks, and leveling up between level 40 and 50. The amount of Rare Candy you get depends on the difficulty of the task, with Raid Battles being the primary source of Rare Candy. You can use Rare Candy on any Pokémon you wish by following these steps: tap the Menu button, tap the Items button, scroll down towards the bottom, and tap on Rare Candy. The best strategy for using Rare Candy will ultimately be your decision to make, as it’s nothing different than any other Candy type. However, it is recommended to use Rare Candy to power up your meta-relevant Pokemon that are difficult to gain adequate amounts of candy for, such as Legendaries.