How to get mew without gameshark or nintendo special event.
Preparations:
Do not fight the youngster with the lv. 17 Slowpoke that is by Bill's house.
Do not battle the trainer on route 8 below the house.
Have a pokemon with you that knows fly
Step 1: Stand here infront of the house and walk forward one step. Step 2: As soon as you see the trainer press start before he has a chance to start walking towards you
to fight you. (This may take some practice) Step 3: Fly to Cerulean City with a pokemon that has been taught the fly HM. Step 4: Then go up the bridge, and find the youngster with the slowpoke. Fight him, but make him walk to
you. That means you have to be at least two steps above him. Defeat him and fly back to lavender. Step 5: Exit lavender through the left (like you are going back to where you started). Your menu will pop up.
Press 'B' and a lv. 7 Mew will appear. Afternote: If you fight different people instead of youngster you will get different pokemon when you do step 5.