Celebi
Celibi is the time travel pokemon. It is better than Mew by far! You can get it at Mall tours or through GameShark.

Flootenkerp
To catch a really rare glitch pokemon that doesn't screw up your game, fly to New Bark Town and go to where your rival stood at the beginning of the game. Press a three times there. Then go to the first patch of grass. Search for about 30 minutes without stopping. Eventually, a pokemon that looks like a mixture of a Mewtwo and a Pikachu will appear. It will be at level 35. You can only catch it with a pokeball and if you use one attack on it it will automatically faint. So throw the pokeball right when you find it. If it doesn't catch it, keep trying. It eventually will.

The Nidoran X
Breed a Nidoran girl and boy and let it hatch a egg. It will be a Nidoran. Keep doing this and get more than more than more than more Nidorans and you will have more Nidorans.

Three legendary dogs tip
First, I will need to say where are the Legendary Dogs. The Lightning one is above of the 7th city WITH the gym. Go to the GRASSY(not water)areas to find it. The Water one is on the left side of the 7th city(GRASSY not WATER). The fire one is on the left side of the 4th city WITH the gym. Go though the guard and go to the GRASSY areas. All of these are level 40. Heres the tip: Each time you see a wild Pokemon, one of the Dogs will change location. So you need to look in your Pokedex and see the new locations they are in. It might be tricky, but its worth it. If you get it, it is like getting instant Level 40

S.S. ANNE ticket
You have to beat the Pokemon League and go to the Prof. to get it. Go to the city with the 6th gym. You will need to go in a underground tunnel to reach the S.S. Anne. The person will check for your ticket and you are off. When you are inside, the sailor will block you from going out. You have to do something and talk to him after. When you are out, you will be in Vermillion City. Get the other 8 badges in the other cities. Tip: Vermillion City gym is even harder than the 8th gym in the other map. Train your Pokemon good.

Fuchsia City Gym Tip
Once you reach to Fuchsia city gym. You will see lots of ningas. Only one of them is the gym leader, and the others are fake. To find out, talk to them. If it is the gym leader, it will stay in the ninga suit. If not, it will show its real person and battle you. Tip: The gym leader is the most EASY gym leader in the map. She carries 5 Pokemon and Each are levels 28 to 30. Easy? Fly will do the best because her Pokemon can kill them self and try to hit you. If you are in the air, it has no effect and the Pokemon FAINTS.

Evolve Onix
To evolve Onix, you need to give it the Silver Coat. I do not know where to find this item, but you need it. The evolved Onix rocks!

Starting Pokemon (Gold version)
Select one of the following to get your first Pokemon:

Chicorita: a Grass type, like Bulbasaur.
Waninoko: a Water type, like Squirtle.
Hinorashi: a Fire type, like Charmander.

Orange League Trainer tactics (Gold version)
Use the following Pokemon types to battle the indicated Trainer:

Itkusi
Neiteio: Use Psychic or Fire type
Slowbro: Use Psychic type
Neiteio: Use Psychic or Fire type
Jynx: Use Psychic type
Exeggutor: Use Fire type

Koga
Araidosu: Use Psychic or Fire type
Venomoth: Use Fire type
Muk: Use Psychic type
Kuroba: Use Psychic or Fire type
Fuoretosu: Use Psychic or Fire type

Bruno
Kaporea: Use Psychic or Grass type
Hitmonchan: Use Psychic type
Hitmonlee: Use Psychic type
Machamp: Use Psychic type
Onix: Use Grass type

Karin
Burakki: Use Psychic or Fire type
Vileplume: Use Fire type
Gengar: Use Psychic type
Yamikarasu: Use Psychic or Fire type
Heruga: Use Psychic or Fire type

Lance
Gyrados: Use Grass type
Dragonite: Use Electric type
Dragonite: Use Electric type
Dragonite: Use Electric type
Aerodactyl: Use Grass type
Charizard: Use Water type

Anno'un Music
While in the Alpha Ruins southeast of Kikyou city go to the Pokegear option in the menu screen. Go to the radio option and on the fourteenth to the twentieth channel you can find a station Called ??????. That is the Ann'oun Music. It can only be heard at Alpha Ruins.

Breeding evolutions
Breed two Pikachus to get Pichu.
Breed two Electabuzzes and you get Eleckid.
Breed two Clefairies and you get Pi.
Breed two Jigglypuffs and you get Pipurin.
Breed two Magmars and you get Magar.

Kirehana
Give Gloom a Solar Stone and it will evolve into a Kirehana. You cannot evolve Kirehana into Vileplume.

Silver Ryhorn
Go to the cave where you go to get to the Elite Five. You should encounter a silver Ryhorn.

Hou-Hou (Silver version)
Go to Pewter City and talk to the old man that walks around. He will give you a gold feather. Then, go to the place where Hou-Hou is located in the Gold version to find it.

Female Mr. Mime (Gold version)
Go to Saffron City before fighting Sabrina. Challenge Sabrina to discover that her Mr. Mime is female.

Monorail ticket
Go to Saffron City and talk to the girl copycat. Fly to Vermilion City and talk to everyone in the house where you received the bike voucher. Someone will give you the Clefairy doll. Take it to the copycat to get the monorail ticket.

Yadoking
Equip Symbol Of King on Slowpoke and trade it into another GameBoy. It will evolve into Yadoking.

Lugia (Silver version)
Learn HM06 (Whirlpool) and go to the place where you received the fifth badge. Destroy a whirlpoor and enter the cave. Go through the maze and you will reach Lugia.

Enjyu City battle (Gold version)
When you go to Enjyu City, go to the tower and your rival will appear, but will not battle. However, if you first heal your Pokemon at the Pokecenter, defeat the Ghost Gym Leader, and then go to that tower, your rival will talk to you and fight