>>500726391) Catch an Abra that knows Teleport
2) Heal at the Cerulean City Pokemon Center to set that as your Teleport warp point
3) Make sure you have not defeated the trainer in the tall grass to the left of Nugget Bridge and the Youngster with the Slowpoke on the way to Bill's House. Make sure you defeat enough of the trainers between Cerulean City and the Youngster, so that you don't trigger a battle with any of them until you can reach the Youngster.
4) Stand one tile above the line of sight of the trainer in the tall grass. Save your game in case you fuck up the next step.
5) Move one step down, triggering the trainer to notice you and try to start a battle. As soon as you move down and before the trainer can start the battle, press Start to bring up the menu. Navigate to the Pokemon menu and use Teleport with Abra. This will prompt the trainer to notice you with the exclamation mark above his head, but you will immediately teleport away before the battle starts.
6) From the Pokemon Center, find the Youngster with the Slowpoke and battle him. Make sure you do not battle anyone else on the way and make sure you step into his line of sight at least one tile away from him, so that he walks towards you. You cannot use the Start menu during this step.
7) Beat the Youngster as normal. You will be able to use the Start menu after this.
8) Teleport back to the Pokemon Center again.
9) Move north towards Nugget Bridge again. When you enter the route, your Start menu will automatically open up without you pressing anything. Close it and it will cause a Wild Pokemon encounter to suddenly start.
10) You can now catch a level 7 Mew.
