Bug: After the S.S. Anne is gone, go to the guard that says that the ship is gone. After facing him, keep pressing right and then quickly push the START button. Save and reset. If everything's OK, you should continue facing right. Select a Pokémon that knows SURF and use this move. Instead of surfing to the right, you'll surf ON the guard! Press down twice, and you'll enter the S.S. Anne again.
Bug: After entering the Cycling Road from the northern gate, go all the way left. You'll see some trees beside the barrier. Then go south, until a point water appears below the trees. If you go up again, you'll see that the trees that were at north have now transformed into water. If you keep going up, and then right so the water is not seen, and then left again, the water has now transformed into trees, again.
Factual error: Go to Cinnabar Island and go to the lab. There are people there who wants to trade Pokemon. Talk to one of them who wants a Raichu. Have a Raichu with you, and trade. After all the trading animation, talk to the man again. He'll say "The Raichu you traded to me went and evolved!". However, in fact, Raichu doesn't evolve into anything.
Continuity mistake: In every gym there is a statue that lists the names of all the people who have won there. The only names that appear are the player character's and their rival's, but when you go to the elite four there are all these other trainers. How did they get past the guards when they don't have any badges?
Other mistake: Being in any route or cave, and then flying or transporting to Cinnabar Island will make the Pokemon of that route and cave appear in Cinnabar's eastern coast, even though they're not water Pokemon and of course don't belong there. This can apply to Safari Zone's Pokemon also, that is, you can go to the Safari Zone, waste your steps there, fly to Cinnabar Island, surf in the coast, and you'll find the Zone's Pokemon there, which can be caught normally, and not with the methods of the Safari Zone (rock, bait).
Other mistake: Go to the Day-Care Man. When he asks you if you want him to care a Pokemon for you, answer NO. He'll say "come again." However, since it is the start of a sentence, it should say "Come" with a capital "C". This happens because "come again" is a shared text, so when you answer YES and put CANCEL, he'll say "All right then, come again." So that's where that text comes from, however, it is still a mistake.
Bug: Go to the hotel in Celadon City. Enter the building and go all right, then go up so you leave a space between you and the little wall. Then press the A button. The menu of a PC will pop-up, as if an invisible PC were there.
Bug: Go to Pallet Town, and go to the northern exit. Cut the grass there with the CUT HM. Enter Route 1 and return to Pallet Town. You'll see, by the sprite of your character, that you're in an invisible grass.
Bug: For this glitch, you must have a Pokemon that knows the SURF HM, and a Pokemon that knows the FLY HM. Go to the old man in Viridian City that shows you how to catch Pokemon. When he asks you if you're in a hurry, answer NO. He'll show you how to catch Pokemon with a Weedle as an example. Fly immediately to Cinnabar Island. Then surf up and down in the coast that's on the right of the island. After some strange Pokemon appear, a weird one, called MissingNo., will appear, which consists of pure blocks of graphics with no sense. Catching this glitch Pokemon can wreck your saved game or glitch your hall of fame. If you make it faint, or just run, you'll have your item in the 6th position 139 times.
Bug: Go to the Safari Zone and enter. Return to the entrance and when they ask you if you want to exit answer NO. Return to the Safari Zone and save, then reset. After loading the file, return to the entrance and they'll ask you to enter the Safari Zone, even though you're already there. Answer NO and leave. Fly to Cinnabar Island and surf in the route that's on the right of the island. After a lot of steps, a ding-dong will appear, returning you to the entrance of Safari Zone with no explanation. Exit, and you'll find yourself in a totally glitch city. The only way to get out of this city is to FLY, so take a Pokemon with this move when performing this glitch.
Bug: Do the MissingNo. glitch and then go to a PC in any Pokemon Center, and select "Pokemon League" in the menu to enter the Hall of Fame (you must have won the League already). When you enter, you'll notice that everything is screwed up, the graphics are just boxes full of graphic glitches, and many weird sounds can be heard. The game may become slow after this.
Factual error: In Cerulean City, there's a man that will trade your Poliwhirl for a Jynx. After trading, he'll say "The POLIWHIRL you traded to me went and evolved!". He may be referring that the trade evolved his Poliwhirl. While there are Pokémon that evolve via trading, Poliwhirl does not. This is a translation mistake from the Japanese Red/Green version, using the Japanese Blue text.
Bug: Go to any of the entrances to the bike route without a bike. Enter to the gate, and then go all up. Now go all left. When you pass right him, he'll say "Excuse me!" because he won't let you advance to the route. However, when he says this, press repeatedly left. You'll go left, and then he'll say that you can not enter the route. Keep pressing left, and you'll eventually enter the route. In this, you'll appear in a bike, even though you don't have one.
Bug: Go to Cinnabar Island without having the Key to the Gym. Surf in the coast that's on the right of the gym, then press left to stand in the entrance of the gym. The usual message "The door is locked" will appear, but if you notice, there's a man in the roof! After the message is shown, the man returns to his normal position in the ground.
Continuity mistake: If you come to Pallet from the south, that is, surfing, you can see that the fat man near the lab will appear out of nowhere when you enter the town.
Bug: At the beginning of the game there's a girl near your house that says she's raising Pokemon too. If you push her to the northern exit of the town, and attempt to exit it, Oak will come and will take to to his lab. Only that this time, because of the girl, you won't be able to follow him correctly and you'll trespass some buildings until finally becoming stuck in his lab's wall.