The Mew Glitch is an old gaming trick dating back to the G/R/B/Y series, mainly used to catch the elusive Mew. The most popular version of this trick is as follows:
1. Cross the Nugget bridge and position yourself above the trainer in the patch of grass next to the water.
3. Walk one tile down into the trainer's veiwspot, but press Start first. If done correctly, your start menu will come up.
4. Teleport or Fly back to Cerulean. As you are about to leave, the trainer gets the exclamation point over his head, but you fly away instead of engage in battle.
5. Go back up the Nugget bridge and find the little boy in the maze toward Bill's house with the level 17 Slowpoke. Battle him and fly back to Cerulean once more.
6. Go back up to the Nugget Bridge one more time. The start menu should pop up. Press B, and the battle music should play and Mew should appear at level 7.
And that is the Mew Glitch!