Breeding Evolutions
At the Daycare Center south of Goldenrod City on Route 33, you can give a male Pokemon and a female Pokemon to the keepers to breed new Pokemon.

Breed two Pikachus to get Pichu.
Breed two Electabuzzes and you get Elekid.
Breed two Clefairies and you get Cleffa.
Breed two Jigglypuffs and you get Igglybuff.
Breed two Magmars and you get Magby.
Breed a Venonat with a Pinsir to get Pinsir.
Breed a Hitmonchan or Hitmonlee with a Ditto to get Tyrogue.
Breed a Clefairy with a Snubbull to get another Snubbul.
Breed a Gyarados with the Red Gyarados to get a golden Magikarp.

Replace any of the Pokemon with the genderless Ditto if you've only got one of a kind. Ditto will act as a wildcard Pokemon.

Duplicate Items/Clone Pokemon
Go to a PC, and save. Attach the item you want to duplicate to the Pokemon you want to clone. Deposit it into the PC. Change boxes. When the screen is saying "Saving the game..." Turn off your GB. Turn it back on. You should have the deposited Pokemon in the PC, and a clone of it in your lineup. The item will either be on both monsters, or in your Backpack. Note: while doing this code, DO NOT withdraw any Pokemon. When the GB is turned back on, you'll find that the withdrawn Pokemon has been deleted. Note: You can duplicate up to 5 items/Pokemon at a time.

Rare Pokemon Locations
Ho-oh -- There is only one Ho-oh in Gold and Silver, so make sure you catch it. You can find it on top of the Tin Tower, but you'll need the Rainbow Wing to go up there. You get the Rainbow Wing from the Radio Station Manager in Goldenrod City (Gold version) or the old man in Pewter City (Silver version).
Lugia -- You can find Lugia in Whirl Island, off Route 41. You'll need to know the HM 06 Whirpool technique to get in as well as the Silver Wing. You can find the latter in Pewter City (Gold) or the Radio Station in Goldenrod City (Silver).
Chikorita, Totodile, Cyndaquil -- These are the three starting Pokemon in Gold/Silver. You have to pick one of the three -- if you want the others, you'll have to trade with a friend.
Entei, Suicune, Raiko -- Dogs, cats, what are they? Who cares! They're cool and they're exceedingly rare. To catch these guys, go to the Burned Tower in Ecruteak City. When you get close to them, they will run away. After this brief encounter, these fast creatures will roam around Johto. So where do you find them? Check your Pokedex and have some Fast Balls ready.
Togepi -- Professor Elm's assistant will give you an egg in Violet City after you beat the Gym Leader there. It will hatch into Togepi.
Tyrogue -- You can get this young Fighting Pokemon from Blackbelt Kyo (if you have an empty slot in your party) in Mt. Mortar, or simply breed one using Hitmonchan or Hitmonlee and a Ditto.
Sudowoodo -- This odd Rock type blocks your way on Route 36 (just like Snorlax). Use the Squirtbottle from Goldenrod City to battle it.
Porygon -- You can get Porygon for 9,999 coins in the Celadon City Game Corner.
Snorlax -- Snorlax is blocking the way into Diglett's Cave. Use the Poke Flute to wake it up.
Eevee -- Apart from winning an Eevee in Pokemon Stadium or the Celadon City Game Corner, you can also get one at Bill's House.
Aerodactyl -- There is only one Aerodactyl in Gold/Silver, but it's not that hard to get. Catch a Chansey and trade with the girl on Route 14 to get it.

Set Your Clock For Daylight-Savings
Return to your house and talk to your mother. She will ask you if you want to set your clock to Daylight-Savings time.

Shiny Pokemon Trick
If you want the full benefit of this code, use a Pokemon that can evolve. Otherwise, there will be some confusion with names and so forth. First, place a flying Pokemon that has been taught FLY as the first Pokemon in your lineup, the "Golden Gyarados" as the sixth position, and the Pokemon whose color is to be changed in the second position. After doing this, put all of the Pokemon back into the PC except the first one. Next, take out the pokemon that was in the second position before, the one that will be changed. Enter the bug-catching contest that is near Kogane city. This is held on Tuesdays, Thursdays, and Saturdays. As soon as you enter it, exit right away. When the clerk asks you if you want to quit, make sure you say NO, which is always the lower answer. Now use your Flying Pokemon to FLY out of the contest. Store the Pokemon that will be changed in a PC, then go back to the contest and say YES, the top answer, to complete the contest. Return to a PC, withdraw the Pokemon, and check its status screen. The Pokemon will be a different color, but it will have Gyarados's name. Grow the Pokemon until it evolves. You may want to use Rare Candies if you have any. Now when you go into battle with the evolved form of the original Pokemon, it will have a shining status.

Solving the Unown Mystery
The ruins of Alph are home to the mysterious Unown (#201), the only Pokemon that exists in more than one shape. Solving the different sliding-tile puzzles will drop you into the ruins below, where you can capture the mysterious Pokemon. In the beginning, you can only access one puzzle (the solution is Kabutop). You can get to the rest of the ruins once you have Surf and Strength. Surf lets you swim to the south cave which contains a puzzle of Aerodactyl. The other two puzzles are reached through the Union Cave using Surf and Strength. The puzzle to the southwest is an Omanyte, while the one to the west is a picture of Ho-oh. The more puzzles you solve, the more varieties of Unown will be available to be caught. (There are 26 variations in all, one for each letter of the English alphabet. Ruins of ALPH, get it?). Once you have caught at least three different shapes of Unown, go to the Alph Lab just outside the first entrance. You will receive an upgrade to your Pokedex that lets you view and collect the different shapes of Unown. Plea. After you have caught all 26 shapes of Unown, you should return to the lab. Using the machine in the corner, you will now be able to use the Unown shapes to create and print out banners using the "Unown font" (if you have a GB Printer).

Special Poke Balls
You can give Apricorns to the Poke Ball maker in Azalea Town to get new types of Poke Balls. Here is a list of what they're good for.

White Apricorn: Fast Ball -- Good for catching Pokemon that try to escape from battle quickly.
Red Apricorn: Level Ball -- If your Pokemon's level is significantly higher than the wild Pokemon's, it will be an easy catch.
Blue Apricorn: Lure Ball -- Good for catching Water types when fishing.
Pink Apricorn: Love Ball -- If the wild Pokemon's gender is opposite that of your Pokemon's you'll have an easier catch.
Black Apricorn: Heavy Ball -- Big enough to catch heavy Pokemon like Snorlax.
Green Apricorn: Friend Ball -- Pokemon caught with Friend Balls will become very attached to their trainer. Good for Chansey (if you want it to evolve into Blissey).
Yellow Apricorn:Moon Ball -- Good for catching Pokemon that evolve with Moon Stones, like Clefairy and Jigglypuff.

Special Trainers
There are six extremely helpful Pokemon trainers in Gold/Silver whose telephone numbers you should definitely keep in your Pokegear. These six will randomly give you tips on how to find rare Pokemon and steer you towards areas where certain Pokemon are currently "swarming."

Fisherman Ralph (Route 32): Helps you find Qwilfish
Hiker Anthony (Route 33): Helps you find Dunsparce
Bug Catcher Arnie (Route 35): Helps you find Yanma
Schoolboy Chad (Route 38): Helps you find Snubbull
Fisherman Wilton (Route 44): Helps you find Remoraid
Hiker Parry (Route 45): Helps you find Marill

Trade Evolutions
There are a couple of Pokemon that only evolve when traded with another trainer. Some trade evolutions also require that the Pokemon holds a certain item when traded. Here's the list:

Kadabra - Alakazam
Graveler - Golem
Haunter - Gengar
Machoke - Machamp
Poliwhirl - Politoed (hold King's Rock)
Onix - Steelix (hold Metal Coat)
Scyther - Scizor (hold Metal Coat)
Porygon - Porygon2 (hold Up-Grade)
Slowpoke - Slowking (hold King's Rock)
Seadra - Kingdra (hold Dragon Scale)

Trade-Only Pokemon
Gold Version: The following Pokemon are not available in Pokemon Gold and have to be traded from Silver, Red, Blue or Yellow:

Bulbasaur, Ivysaur and Venusaur
Squirtle, Wartortle and Blastoise
Charmander, Charmeleon and Charizard
Kabuto and Kabutops
Omanyte and Omastar
Vulpix and Ninetales
Meowth and Persian
Phanpy and Donphan
Ledyba and Ledian
Skarmory
Delibird
Articuno
Zapdos
Moltres
Mewtwo
Mew

Silver Version: The following Pokemon are not available in Pokemon Silver and have to be traded from Gold, Red, Blue or Yellow:

Bulbasaur, Ivysaur and Venusaur
Squirtle, Wartortle and Blastoise
Charmander, Charmeleon and Charizard
Kabuto and Kabutops
Omanyte and Omastar
Mankey and Primeape
Growlithe and Arcanine
Teddiursa and Ursaring
Spinarak and Ariados
Gligar
Mantine
Articuno
Zapdos
Moltres
Mewtwo
Mew

Unown Music
While in the Ruins of Alpha 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 Unown Music. It can only be heard here.