Raikou is an Electric-typeLegendaryPokémon that was introduced in Generation II. It is known as the 'Thunder Pokémon' and is a member of the three legendary beasts along with Entei and Suicune resurrected by Ho-Oh.
How to Obtain
Raikou can be found anywhere, anytime.
Upon purchasing the gamepass, you can go to Viridian City and talk to the guy in blue at the PokeMart and he'll give you a random legendary beast. (Raikou, Entei, or Suicune)