Hi!! I've updated this section quite a lot of times already now.  Try these codes at your own risk.  I haven't had time to try them all out so some of there might be a slight chance some of them wouldn't work.  These codes aren't in any particular order or anything like that.  All of them are for the American version (besides the Mew code). Anyways, if you have anything that you want to contribute here, feel free to e-mail me.  Check back soon!
 

Note: It might be helpful to see the Miscellaneous Game Info section for stuff like which Pokémon are available on which pak and more. Another helpful place would be to look in the Item List section too. For help on the Gym Leaders and the Elite Four, click here.
 
 
 

To get Mew (151th Pokémon):
Although Nintendo themselves say that you cannot get Mew, or Myuu, in the US version, some sites have claimed that they've catched Mew in the Japanese version.  I heard that he's in the cave where you can get Mewtwo.  A site (This is for the Japanese version) said you have to go to Shion Town and ask the nickname changer to change your Koiking's nickname to Mew. Go into your tools, go down to the 13th tool and click SELECT at least 8 times. Now ask the nickname changer to change the Koiking's nickname again. The monster will blink, the changer won't do it and you have Mew!
To gain experience faster:
To easily gain experience, use the Pokémon you want to train with the top Pokémon on your list. When you go into battle the Pokémon will pop out. You can then switch to another Pokémon. Once you win the battle the beginning Pokémon and the fighting Pokémon will both gain experience points.

(GameSages website: Submitted by Brian Conrad ([email protected])
 

Easier way of catching Pokémons:
When  you  are  trying  to  catch a Pokémon, after sending a Pokéball, hit the A button while  repeatedly pressing the right arrow key. If it doesn't work the  first couple of times keep trying, it should work after a practice shots.

Submitted by Dave Hallam ([email protected])
 
Some GameShark Codes:
Infinite Money: 01ff16d0
No Wild Pokémon battles: 01033cd1
Infinite HP: 019947d3     019948d3     019949d3

Submitted by [email protected]

GameShark Code for Mew:
0115d8cf
To start with Mew: 01151ed1

Pokémon No. 000:
If you use one Japanese version and one American version to trade. Trade 3 Times
and the American Version will get Pokemon No 000. So there are actually 152 Pokemon. Pokemon No 000 is level 254, but he doesn't obey you at all even if you have Giovanni's Earth Badge.

Master Ball Cheat:
When you throw a Great Ball, hold UP and B. This will make it act like a Master Ball.

Saving money in Pokémarts:
If you want to buy a large amount of one item buy three. You will discover that buying items in groups of three is free or the store pays for. I got many expensive items like this.
Note: This trick only works in certain marts and only on certain items.

Submitted by [email protected]

Secret Coins:
There are hidden coins lying around in the Game Corner. You can pick them up by
walking around and pressing the A button.

How to move Snorlax:
First, you must go to the Casino place with the slot machines and there is a team rocket member in the back. Talk to him and then you'll fight him. After, press 'A' on the picture behind him: this will open a secret door. Go through the secret door, beat the building and you will get a Silph scope. Go back to the place with the ghosts and go in that tower. Go all the way to the top then you'll fight Cubone mothers which you can now see because you have the Silph scope. Then go up fight the team rocket members. After that, talk to the guy you rescue and he'll give you the Pokéflute!! The Pokéflute will help wake up Snorlax

Celadon City Slot Tip:
All of the slot machines have different odds, which change every time. Play each
machine 4 times, and if it hits 2 or more, then stick with that one, because it's probably hot.
If the slow machine forces you really close to a 777 or Bar Bar Bar it will probably give you one or the other soon.
 
(GameSages website: Submitted by [email protected]
 
The following codes were sent by Paolo Gaspar ([email protected]) Thanx!!
 
To catch Spearow and Nidoran in Viridian City:
In Viridian City, go left towards Victory Road. On the tall grass, you can catch Nidoran and Spearow during this early part of the game!!

Where to find the rarest Pokémon:
Articuno: He's an ice Pokémon and is found in the Seafoam caves. To reach him, you have to push to rocks into those black squares. They will fall into water and change the current. After the current is calmer, use the surf ability to reach the island with a bird on it. That's Articuno. Make sure you have ultra balls with you, you have only one chance to catch this Pokémon.

Zapdos: He's an electric type Pokémon and is found in the Power Plant under Rock cave. Use the surf ability to reach it. Go into the river and just follow the only path. Search around the power plant. It's like the others, a bird. You have only one chance, so be careful.

Getting through Victory Road:
NOTE: you need a Pokemon that knows the strength technique to move the boulders that are found inside.
Go to the left and move the boulder onto the switch to the right, the switches look like little round things. Now go up the stairs onto the ledge and get off the ledge using the stairs on the left side. You will now see a ladder with a trainer standing next to it, go down this ladder. After going down the ladder walk down and you will see another boulder and switch, move this boulder over the switch. Now go up onto the ledge and follow it, on the other end get off. Once off the ledge move right and you will see a wall, now move up all the way, then move left. Go down the ladder. YOu should now be on a new level and you should see a boulder, do not move the boulder yet. Go up and then move left, keep going until you see a little 'room' with a switch and a ladder in it, this is the switch that you're supposed to put the boulder on. After putting the boulder on the switch, go back to the ladder you came from. DO NOT GO DOWN THE LADDER. What you need to do then is walk onto the ledge that you see and follow it and go down the stairs on the other end of the ledge. After getting off the ledge, go all the way left and you will see a boulder with a hole next to it (like the kind you find in Seafome Island). Drop the boulder into this hole and then go down the hole yourself. Now go onto the right side of the boulder and begin pushing the boulder all the way to the left until you can't go any further. Put the boulder onto the switch that you see. Now go up onto the ledge and you will see a ladder, go down this ladder. Now move up and go down the other ladder and *viola*, you're at the Victory Road exit!

Here is a list of rare Pokémons, stats, catching strategy and locations:
Articuno
Type: Ice
Level: 50
Catching strategy: Have any normal type at L: 45-51. Reduce life less than half. Use ultra ball to capture.
Location: Seafoam Islands
Rank: 2nd

Snorlax:
Type: Normal
Level: 30
First beat them up when he uses rest reduce under half and use Wiggytuff to put him to sleep then use an ultra ball to capture.
Location: Before cycling road.
Rank: 150th

Zapdos:
Type: Electricity
Level: 50
Use Articuno's ice beam then use a master ball to capture.
Location: Power Plant
Rank: 3rd
 

Moltres:
Moltres is in the victory road cave on the third level from the entrance (bottom I think) and Mewtwo is in the cave outside of Cerulean that only Pokémon champs can enter. For catching them, weaken them then put them to sleep this is the best way to catch them if you do not have the master ball.
 

Find Mewtwo:
To find the ominous "Mewtwo", go to Cerulean City and travel up the bridge toward Bill's. When you reach the end of the bridge, go to the left and us the surf ability. Follow the river until you reach a cave. This is the unknown dungeon, (like it says in the map in the instructions).  Now, travel through it to find Mewtwo. He's at level 70!!! Remember: You get one chance.

For other rare Pokémon, try the safari game in Fuschia city. To catch them, first throw bait, then a rock, and finally the safari ball. The ones hardest to catch are the weaker ones, because they always run. (how annoying)

 
Getting a Metapod, or a Kakuna, that can attack:
First, you must capture a Caterpie , or a Weedle, before they're in level 7 (level 7 is when they evolve into Metapod/Kakuna) *Note: In doing this, you do not get Harden.*  Yet another note: They will only stay in Kakuna/Metapod for three levels,after that you get Butterfree/Beedrill.
 
The Golden Teeth:
In the Pokémon instruction manual, it tells about golden teeth. They are located in Safari Zone near the Secret House.

To get to the Power Plant for Electric Pokémons:
Go to Cerrulean City, head toward Saffron but don't go to Saffron. Instead, take the path that leads East toward Rock Tunnel. Don't go into Rock Tunnel, instead go North to the water and SURF. It will lead you to Power Plant. Be Careful, some of the things that look like Poke Balls are actually Voltorbs.
 
To defeat Ghosts in Lavender Town:
In Lavender Town, to defeat the Ghosts use a Poke Doll. You can get one from Celadon Dept. Store.
 

Finding Electric-type Pokémons:
If you are looking for electric type Pokémon, don't sweat it.  Go to the entrance of rock tunnel (by Cerulean city) and use the surf ability at the river nearby. Just follow the only path, that will take you to an old power plant. You will find Many Voltorbs, Medium Pikachu's, Medium Magnemite, Few Raichu's and VERY Few Electrodes.
Note: Electrodes will always use self-destruct, it's easier to trade a
Raichu for an Electrode at the Cinabar Islands.

In case you didn't know...
Traded or released Pokémon still count as yours in the Pokédex. If you traded Spearow, the Pokédex will still have all the info on Spearow, so don't worry about recatching one. This will also work with game link cables. Trade the Pokémon with your friend, get the info, and then trade back.
 
Getting a free bike:
In Vermilion City, there is a Pokémon fan club. If you listen to what the Club President says, he'll eventually give you a Bike Voucher. Take it to the Bike Shop in Cerulean City to get a bike for free! This saves a LOT of time trying to earn money to buy it!

Where the 5 Moon Stones located:
1. In the upper-left-hand corner of the first area of Mt. Moon.
2. In the basement of the Game Corner in Celadon City.
3. In the bottom right area of Route 2 (need CUT)
4. In the burnt down building on Cinnabar Island, check the pillars (face it and press A) on the first floor.
5. Go into Mt. Moon, then go right before the Supernerd (you battled him to get a fossil, remember?) Look to your right, there should be a corridor (about 4-5 spaces long, and 1 space wide. Press the A button at the end and it will say you found a moonstone! Thanx for Mike for this one!!
 
Better way of catching Dratinis:
To better catch Dratinis, you have to catch at least one.  Once you have one, leave the Safari Zone.  Come back again (with the Super Rod, mind you) and go to any body of water. The closet one will work.  Use the Super Rod, but HOLD "A" when it says USE/TOSS.  Then,  your chances of catching a Water Pokemon are increased, though you might get, "Not even a nibble!" a few times.  I'm not 100% guranteeing that you will get Dratini, but you have high chances.
Another way to do it is:
Go into the Safari Zone and fish with the Super Rod.  If you already have a Dratini, they become more common.  Wait a while because it takes a while.  Also, if you lose Dratini, it helps to go to another body of water and fish again.  This trick does not always work, so be sure to try it more than once.
Submitted by "Charmie" and Meepiuu
 
The following codes were sent in by [email protected]
Thanx!!
 
Fight Safari Pokémon Elsewhere:
Here's a trick that allows you to fight Pokémon from one area of the game, to another area! Don't get it? Listen up! Here's an example on how to do it: That annoying place where you catch the good Pokémon, yep, the Safari Zone!! Go there and battle for a while. Lets say, you can't catch a Tauros, fight one, then leave the Safari Zone.  After, go to the island where Articuno is found, Seafoam Island I believe, and swim up to the shore.  Now, swim up and down the shore, where it looks like you're on the ground, but your swimming in the water, and you'll fight monsters from the Safari zone!  No more rocks and bait, its Psychic and Psybeam time!  If you don't know what spot Im talking about, here's how you get there; go to the shore of the town that has the Safari zone (just go straight down from Pokémon Centre) and go against the left wall when you hit water, use surf, and swim against the wall down then left until you reach the first shore you see, which is Seafoam Island then just go up and down as I said before and kick Pokémon butt!
 
Unlimited chances to catch rare Pokémon:
Did you ever run into one of those Pokémon that you can only catch once? Here is a good trick to get as many shots as you want to catch those Pokémon! First, find a rare Pokémon, such as a Mewtwo. Then, right before you go into battle with it, save the game at that point. Finally, you can battle the Pokémon without worrying that you didn't catch it. If you screw up and you make it faint, just stop where you are and shut off the game. Then you can turn it back on, select continue and presto! You should be saved right before getting into battle with the Pokémon!

Unlimited Time for Safari Zone (Water Pokémon only):
Did you ever want to catch a Pokémon at the Safari Zone, but always run out of time? If it was a water Pokémon, you're in luck! This trick gives you Unlimited Time in the Safari Zone to catch water Pokémon.  First off, you may want to get a Good Rod or a Super Rod. Next, go to the Safari Zone and go to some water. Then, go into your items and use the rod. It should start fishing. If you get a message that says "Not even a nibble", press A and then quickly press start. If you got into a fight, check the Pokémon out. If it is one you don't have catch it and then quickly press start after the battle and go back into your items and fish again. If you already have this Pokémon, run from it and then quickly press start and start fishing again. This will help you catch some good water Pokémon and have plenty of time to do it.

Unlimited Time for Safari Zone (Water Pokémon only):
(Different from above)
In the Safari Zone, go fishing next to any pond. All you have to do is stand still, don't fish anywhere else, and you will do fine. The time only goes down when you walk. This is stated on one of the signs in the Safari Zone.

This code was submitted by Brandon Duckett

Harder Hitting Attacks:
This code is sorta like the "Better Chance to Catch Pokémon" code but it's for attack. Just hold the A button while your attacking and it will do more damage than if you didn't hold A.
 
How to Defeat Sabrina - Saffron City Gym
When you enter the Saffron City gym you'll see a warp next to a trainer. Step into it. You'll appear in another room full of warps and a Trainer. Step into the warp on your left. Then step into the warp below you. Then step into the warp on your left. And then, step into the warp on your left.
    Once done that, you'll come in to a room with one warp and that's the one your
standing on. Now talk to the trainer in the room, and get ready to defeat Sabrina.
Here are the Pokémon she will use:

    Kadabra - L38
    MR. MIME - L37
    Venomoth - L38
    Alakazam - L43

These are all psychic Pokémon and very powerful. Your best bet against these guys
is a Venusaur or any other grass-type Pokémon. Use your Razor Leaf if you have a Venusaur. If you win you'll receive her Marsh Badge which will ensure any Pokémon up to L70 will obey you. You'll also get a TM46.
 
(GameSages website: Submitted by Ramkrish Raja)
 
Clone Pokémon (US version)
You need a friend for this. Trade the Pokémon to be cloned and have you friend
get a Pokémon they don't care about. Trade them, and make sure the person getting the bad Pokémon can see the other's screen. When the receiver of the good Pokémon's screen says "waiting", get ready to shut the other one off. When the waiting disappears, turn off the Game Boy that's getting the bad Pokémon. When the other one says trade completed, turn that one off too. When you turn the games back on, you should both have the Pokémon.

Warning: This could erase you game so be careful.

Easier way of catching Abra:
The first thing Abra does is teleport so it's obviously really hard to weaken it.  Use the Warp attack with Ekans. With that, Abra couldn't move and I was able to weaken it enough to catch it. This works with Bellsprout in the blue version.  If your Ekans or Bellsprout can't attack before Abra teleports, then your monster needs to gain more levels in order to increase it's speed. Abra is very useful because it can teleport you to the last Pokémon Centre you were at.  When it evolves into Kadabra, it is very powerful against a lot of enemies that you meet later in the game.