Mew Glitch

Hi all, I'm here to talk about the mew glitch. Please enjoy!

The mew glitch (gen. 1.) is known for its ability to help you catch non-glitch Pokemon, especially Mew.
Mew glitch pic taken from Bulbapedia.

Using the Mew glitch causes a lv.5 Mew to appear.

The earliest point you can obtain the Mew is after you have defeated the Swimmer in Cerculean Gym.
The Player must have an Abra that can teleport.

"With an Abra in their party, the player then needs to stand north of the Jr. Trainer so that he is just below the screen. It is recommended that the player now saves the game. The player must move down until seen and immediately press the "START" button. The player then needs to Teleport with Abra. If done correctly, the Jr. Trainer should get the indicative exclamation mark above his head immediately before the player Teleports. At this point, the menu will not work until after the player enters a battle, though it is imperative to not battle.
The player then needs to head east from the Pokémon Center into the Cerulean Gym and battle the Swimmer. After defeating the Swimmer (the menu should be available upon victory), the player then must head to Route 24, and after several steps the menu will appear. Upon closing of the menu, a battle will begin with a wild Mew."
- Bulbapedia

Hope you enjoyed this!