Other mistake: If you don't have the Silph Scope, you'll run into GHOSTs at the Pokemon Tower. However, in the middle of the battle, if you see any of your Pokemon's stats, and then return to the battle, the GHOST will be gone and you'll be able to see the real Pokemon behind it.
Other mistake: Go to the item list, and select any HM. Attempt to use it on a Pokemon. Before you do, the text below will say "Use TM in which Pokemon?" However, you are attempting to use a HM, not a TM, on a Pokemon.
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.
Other mistake: When taking the first step into Route 24, press Start. The first trainer of the Nugget Bridge will be standing in the water until you press Start again.
Other mistake: Between Viridian's forest southern and northern gates, there's a whole forest, but judging by the scenario shown outside the forest, it appears that between the gates there's just normal road.
Other mistake: Before winning the League, go to the man that doesn't let you enter to the Unknown Dungeon (Cerulean Cave). Go some steps to the left until you exit the city. Now look, that man has disappeared. If you return to the city, the man's there again.
Other mistake: Get a Pokémon with a Special of 21, and with a move that increases its Attack (as Swords Dance, TM03). Now do the Mew glitch, that is, fly or somehow escape at the same time one trainer sees you by scrolling the screen. Fight with any trainer, then go to Route 13, 14, 15 or 16 and search for a Ditto. Let the Ditto transform into your Pokemon with Special of 21. Now, wait for it to use the move that will increase its attack. It has to use it at least three times. Return to the route where you escaped the trainer. The menu will pop-up, exit and you'll encounter a Mew, however, it will be at least in level 10, and it will know TRANSFORM. Let it transform any of your Pokémon. Then catch it. The game will say you caught a Ditto, not a Mew. The Mew will be gone forever, and instead the Pokémon will be a Ditto.
Other mistake: Marowak's ghost is supposed to be avoided only with the Silph Scope. However if you use a Poke doll in his battle it'll escape and you can proceed the game. This makes no sense whatsoever, because if you do that and advance through the game, you'll find Giovainni with strong Pokemon, but if you go later to get the Silph Scope, Giovainni will be there with weaker Pokemon. Big part of the game can be skipped with this glitch.
Other mistake: If you get all the Pokemon and talk to Oak, he'll say "Your POKEDEX is entirely complete Congratulations!". Between "complete" and "congratulations", there should be a period.
