Mew Glitch
This is a glitch used to encounter Mew, which cannot be found in normal gameplay. You must have some way of transprtation, such as a Pokemon with Fly or a Pokemon that knows Teleport. You must not have defeated the Jr. Trainer in the grass on Route 24, and the Swimmer in Cerulean Gym or the Youngster in Route 24 must be open for battle, and the trainers in the way of them must be defeated. First you must position yourself so that you are above the Jr. Trainer amd he is just out of your sight. You might want to save now in case you mess up, because this next part is tricky. Now you must press the down button, and the next instant, while you are holding down the down button, press start. If done correctly, it will bring up the start menu while you are in the sight of the Jr. Trainer. Now use your method of transportation to go to Cerulean City. You should see an exclamation point above the Jr, Trainer's head, but you will go away before he can walk up to him. You will find that you cannot open your start menu. Go to either the Youngster in Route 24 or the Swimmer in Cerulean Gym and battle him. Walk to Nugget Bridge and your menu will pop up. Press B to get out of the menu and you will battle Mew!