A bit of common sense people, if mega mew is asking how to beat Misty, chances are s/he is at Misty and cannot go back for a Pikachu. Since beating Misty isn't an instant necessity the moment you reach Cerulean, fight Gary, catch a Bellsprout/Oddish, wrap around through Bill's House, go to Vermilion City, catch more pokemon around there, train them all up of the boat, THEN go back and fight Misty.
And you may want to turn your Caps Lock off.