Blue Version

The version of the game defines whether some Pokemon are catchable or not.

In the Blue Version you can find:

027Sandshrew2Sandshrew 069Bellsprout2Bellsprout 037Vulpix2Vulpix 126Magmar2Magmar 127Pinsir2Pinsir

and you can't find:

023Ekans2Ekans 043Oddish2Oddish 058Growlithe2Growlithe 123Scyther2Scyther 125Electabuzz2Electabuzz

which are only obtainable in the Red Version.

The version also makes it more likely to find some pokemon in the wild:

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