Must be able and know how to do the Glitch City glitch. Being able to either Fly (better) or Teleport
Walk around in the Safari Zone until you have a low number of steps left (40 is correct) Walk out, say 'No' to the "Leaving early?" message, save and reset, walk out and say 'No' to the "Would you like to join the hunt?" message. Fly or Teleport to Pewter City, walk to the NPC next to the PokéMart and talk to him. Say no to his "Did you check out the MUSEUM?" message to make him walk you to the Pewter Museum of Science. The aim is to run out of Safari Zone steps while he is still escorting you to the museum. You will receive the PA: Ding-dong! Time's up! Your SAFARI GAME is over!" message and be taken to the Safari Zone gate. Step out of the Safari Zone gate to walk out of Pewter City's exit 04 - the Pewter City PokéMart. As you arrive, you'll receive the "It's right here! You have to pay to get in, but it it's worth it! See you around!" message. Save and reset. Walk to the Pokémon Center and the NPC should be walking downwards in a line through the Pokémon Center door. He will loop through to the top of the screen from the bottom of the screen as well. Talk to him from the right just below the Pokémon Center door and say 'NO' to his message again. You will walk automatically and the menu should keep popping up. Hold B when the menu is closed to walk around in any direction but down.
If you Fly away, you'll be able to walk down again and you can walk anywhere while holding B until you enter a door or battle a Trainer.
Method 21. From Pewter City Poké Mart, use dry underflow glitch to underflow the number of stored PC items to 255.
2. Place a Master Ball at PC item 95
3. Save and reset
4. Walk out of the Pokémon Center and speak to the museum guy from the right just below the Pokémon Center door. If you do not succeed at talking to him, reset the game and try again.