In Pokémon Ash Grey, The story closely follows that of the Anime, including for example, the situation with Spearow in the very first episode, that formed the close bond between Pikachu and Ash.
The game is fairly similar to the other official games, including random encounters in grass. After getting to Viridian City, you can then re-visit Route 1, to train or capture Pokémon. However, all I've managed to run into so far are Spearow, and one Pidgey (which I caught).
Are these the only Pokémon in the area? Or does the game allow all pokemon seen on that route in the Anime to be caught?
Note: In the Anime, there was a Rattatta digging through Ash's bag, as well as a montage of other Pokémon including Mankey whilst Ash was running away from Spearow, and even a Gyarados at one stage when Ash was underwater.