Other mistake: Go to the Day-Care Man. When he asks you if you want him to care a Pokemon for you, answer YES, but in the Pokemon list, press B to cancel. He'll say "All right then, Come again." However, the "Come" shouldn't be capitalized, it should be "come". This happens because this is a shared text, so when you answer NO to his question, he'll say "Come again", and that's why it is capitalized for this text. However, it is still a mistake. This was made due to a similar text error in Red/Blue, but this mistake was created.
Bug: Go to Bill's house. Before you enter the door, watch quickly at the back of his house. You'll see a mountain without the usual border.
Other mistake: At the beginning of the game, Oak gives you a Pikachu. By this time, Pikachu is in a Pokeball. When you fight against Gary, however, the Pikachu doesn't come out of a Pokeball, like in the rest of the game. However, in this battle, he should come out of his Pokeball.
Bug: For this glitch, advance through the game until you get the FLY HM and get a Pokemon that can learn how to fly. Also, do not fight the trainer in the Cape that only has a Slowpoke, nor the trainer that is looking up outside the Underground Path (right entrance). Go to this entrance of the Underground Path and face down. Press down and immediately press Start. You'll be in the trainer's sighting, but he won't react to this. Go to Pokemon, choose the Pokemon that knows how to Fly and fly to Cerulean City. The trainer will now notice you, but you'll fly away. In Cerulean City, the Start menu won't work. Now go to the Cape and let the Slowpoke trainer see you and walk to you. Defeat his Slowpoke and the Start menu will work again. Fly to Lavender town, and go to the route that heads to the left. When you enter the route, the Start button will pop up for no reason. Press B, and a wild Pokemon animation will show up. From nowhere, a Mew, an impossible-to-get Pokemon, will want to fight with you.
Plot hole: If you use a Pokedoll against the Marowak Ghost in the Pokemon Tower, you can actually skip the battle and progress through the game, without ever getting the Silph Scope. This make no sense, you skip a large portion of the game this way. Just as an example, after skipping the Ghost, you fight Jesse and James with evolved Pokemon, but if you go to get the Silph Scope after this, they will be there, with unevolved Pokemon.Dr. James