There is only one way to get Mew without using GameShark. When you get to Vermillion City, trade somebody for a Pokémon that knows surf and a Pokémon that knows strength. Now go past the guy that checks to see if you have a ticket, but don't go on the S.S Anne. Instead, surf off to the left and you will come to Cinnibar Island. There will be a truck in the way which you need to move out of the way using strength. Mew is behind the truck.
When your Pokémon is just about to attack, hold down the A button. This will make your attacks more effective.
First, go into items and press A on the rod you want to use. Now, hold A when it says USE/TOSS. Your chances of catching a water Pokémon are now increased.
In case you were wondering why your itemfinder was going nuts in the Rocket Game Corner (or even if you weren't) there are secret coins hidden inside the Game Corner.
You can pick them up by walking around and pressing A. One paticularly large amount, 100 coins, is hiding right above the second row of slot machines from the right. Now how the heck can someone drop 100 coins on the floor and not know it...................?
First, trade two Pokémon that both people want but neither is willing to give it away. As soon as the screen says "Trade Completed" turn off both game boys. Be careful, because if you turn off your game boy too soon, your game may get erased. I learned this the hard way.
For this code, you will need a pokémon that knows FLY, a pokemon that knows surf, and access to Cinnibar Island. you should also have your highest-level pokemon with you. Now take the item you want to have 129 of and make it your sixth item with all items that don't have an x1in front of them. (The item you want to have 129 of has to be an item that has an x1 in front of it) Now, Walk or FLY to Viridian City. Talk to the guy who wouldn't let you through before. (The one that shows you how to catch a Weedle) When he asks you if you're in a hurry, say NO. Now wait until he's finished catching the Weedle and then FLY to Cinnibar Island.Walk to the right edge edge and SURF up and down the very shore. You will encounter various pokémon, including ones over level 100 and Missingno. (His name will either be Missingno. or some other screwed up name depending on how far you are in the game) Either kill him or run from him. You will now have 129 of your sixth item. DO NOT CATCH MISSINGNO!!!! (For more details, consult the FAQs.
Before charging into battle with a trainer or a pokémon that you'll never have the chance to try to catch again, DON'T FORGET TO SAVE THE GAME!!! You don't want to kill that highly desirable Mewtwo you so desprately wanted or just barely lose to your Rival, be forced to turn off your game and end up not even halfway as far as you were when you blacked out!!! (Save your game often, also, just in case your batteries go dead on you.)
I haven't confirmed this code yet , but some people claimed that they got a Pikablu in Red/Blue versions this way. First, get a Raichu up to level 90. Next, give it to the guy at the day care center. Wait until your Raichu has grown to level 100 and get it back. When you ask the guy, he'll say that your Raichu ran away and he'll give you a Pikablu instead. Pretty cool, huh?
You really want that pokémon your friend has but he's not willing to risk the cloning code? We have a solution for that. First, fight your friend in a link cable battle in which he only uses that Pokémon. When the battle's over, FLY to Cinnibar Island if you're not already there and SURF up and down it's right shore. You will find that Pokémon you wanted. This works well with a Mew, also.