>>20366093Eevee was considered as well however - and stood a better chance than clefairy.
And honestly, between the three, Pikachu's the most unique creature anyhow:
Eevee looks too much like any other cute critter and well, it's brown.
Clefairy would have been altered slightly to appeal more to the boy demographic even if it was picked - see: that weird gag manga with the Clefairy. There are many things you could call that thing and femnine is not one of them. Plus it looks too similar to other Magical Girl critters like Mokona in Magic Knight Rayearth which was popular at the time.
Pikachu is the clear winner - and was one of the early sought after monsters in the early game by most players - since it was the first rare mon with a unique type for about half the game - the next electric type would be voltorb which didn't show up until after the third gym.
Though yes, I would have liked Poliwhirl as a mascot
and I'm sure if Satoshi Tajiri had his way it would have been 
