1. Lapras
Pokémon Go's New Water Event Makes The Rare Lapras More Common.If you’re still waiting for Lapras to land in your Pokémon Go PokeDex, it might be your lucky day.
2. Golden Magikarp and Gyarados
The rarest Pokémon of them all, it would seem, is the golden Magikarp and red Gyarados, apparently the only "shiny" Pokémon in the game at the moment and now one of the most sought after trophies in the game. Shiny Pokémon are rare color variants of standard Pokémon -- they don't get combat bonuses, but they're nice to look at it. In the main game, shiny Pokémon occur only in about 1 in 4000 creatures, but it's unclear just how rare they are in Pokémon GO.
Beyond that, however, there are plenty of other prizes on offer. Gyarados -- red or otherwise -- has been an endgame Pokémon for a lot of players for a while now, considering the colossal number of Magikarp candies it takes to get one and how rare they are in the wild.
3. Blastoise and Feraligatr
Pokémon such as Squirtle and Totodile are not quite as uncommon those other ones mentioned, though it takes a lot of them to get some third-tier evolutions, and so many players might appreciate being able to accelerate progress towards a Blastoise or a Feraligatr.