Pokemon Red and Blue is the original pokemon game where you can only catch 150 pokemon and have to trade for some.

Here's a list of pokemon you can get in one game but you can't get in the other take a look!

Red --------- Blue
------------ - ------------
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Scyther --- Magmar
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Electabuzz --- Pinsir
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Mankey,Primeape --- Sandshrew,Sandslash
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Ekans,Arbok --- Meowth,Persian
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Oddish,gloom,vileplume---Bellsprout,weepinbel,Victreebell
Growlithe,Arcanine--- Vulpix,Ninetales