How do you catch all 151 Pokemon in Pokemon Yellow without trading?

Answer 1

You cannot catch all 151 Pokemon without trading or cheating for them. Weedle, Kakuna, Beedrill, Ekans, Arbok, Raichu, Mewoth, Persian, Koffing, Wheezing, Jynx, Electabuzz, Magmar Gengar, Machamp, and Alakazam must be obtained through trading.

For the Mew glitch in Pokemon Yellow, you should start over, if you did encounter the Gambler on Route 8 or the Youngster by Route 25. Go to the Underground Path, but go in front of the door, not inside the tiny building. (Save first) Take one step down and instantly press Start. Go to your Pokemon, then select on the Pokemon that knows Fly, then fly to Cerulean City. The Gambler should have the "!" appear above his head as you are about to leave.

When you arrive in front of Cerulean City's Pokemon Center, head north and across the bridge. You may notice your Start button is disabled and no menu pops up. This is normal and this means you are doing this correctly. Reach the Youngster with a Slowpoke, then defeat his Slowpoke. Your menu should appear again. You must Fly to Lavender Town and head east to Route 8. A menu will appear, so you will need to press B. Mew will appear as level 7 with just the move Pound. This is the only legendary that is not naturally in Pokemon Yellow.