There's a rumor that if you visit the route north of Cerulean City to talk to a trainer that's always sitting by Bill's house, then immediately proceed to head to the western city limits of Lavender Town towards Route 7, you may encounter a Mew.

It's also rumored that this Mew may know thief and it may have the ability to use items found in your bag on you. Are the rumors true? No one is quite sure, since no human has been able to confirm them.

Arcanine Transfur for  Terri_the_Dragon