Complex sentence: Ekans began as an exclusive to Pokémon Red, and could not be caught in Pokémon Blue or Pokémon Yellow, but it could be found in Pokémon Gold, where it can be bought at the Goldenrod Game Corner.
Split into simpler sentences: Ekans began as an exclusive to Pokémon Red, and could not be cought in Pokémon Blue or Pokémon Yellow. In Pokémon Gold, it can be bought at the Goldenrod Game Corner.