Mount Moon Mondays

Go back to the pond at Mount Moon at 8 PM on Mondays. You'll be treated to a scene in which Clefaries dance around the pond, and then leave. However, it changes the encounter rate/stats of Pokemon found within the pond. If you use Surf, there will be a 100% encounter rate for Poliwags. If you use the Super Rod, you'll be able to catch Magikarps that are up to Level 40, instead of the regular Level 20.

Contributed by: discoinferno84 

Pomeg Berry Glitch

For this glitch to work properly, you must have a Pomeg Berry and a Pokemon who has not had their HP lowered as much as possible already through Pomeg Berries. (If the latter is the case, the use of HP Ups on the Pokemon will suffice.) Get the Pokemon to a severely low level of HP (1 or 2 HP). Once you do so, in the field, use the Pomeg Berry on the Pokemon. This will in turn cause the data in their HP to cycle back to the top of the counter, giving the affected Pokemon 65,535 HP - over 90 times the otherwise possible maximum in the game.

Contributed by: Anonymous 

Level Up Unhatched Pokemon

To do this glitch, you must first execute the Pomeg Berry Glitch, which is done by using a Pomeg Berry on a Pokemon with 1 or 2 HP so that its HP loops to 65,535 (displayed as ?35 in-game). Do so, however, with only one Pokemon and an Egg in the party, with the Egg in the top-leftmost slot of the party in the Pokemon menu. After executing the glitch, you will now be able to enter battles and use the Pokemon Egg as if it were a normal Pokemon. It will function as a normal Pokemon - you can view the stats it will have upon hatching, it can level-up by beating Pokemon, it can learn new moves, it can even evolve. This means that you can alter the Pokemon inside the Egg in otherwise-illegitimate ways. For example. Pikachu cannot normally know Thunder when hatching from an Egg at Level 5; through this glitch, Pikachu can. Similarly, you can hatch Eggs with fully-evolved Pokemon such as Typhlosion, Meganium, and so on, inside.

Contributed by: Anonymous 

Unlock 8 bit music

Once you obtain all 16 badges, talk to the music designer in Celadon, and you unlock the 8-bit originals from the original gold/silver games.

Contributed by: big_one12 

Diamond Dust

On the following days, Fly up to Mt. Silver and instead of your usual snowfall, there will be glittery diamond snow:

February 29th (leap year day)
March 15th (Ides of March / Honen Matsuri)
October 10th (release of Pokemon Blue in Japan)
December 31st (New Year's Eve)

Contributed by: Anonymous 

Red Gyarados, Shallow Water

Your encounter with Red Gyarados at Lake of Rage is required to progress the story. Most players see the Shiny Pokemon, catch it because it's so rare, and move on. The lake will have shallow water every Wednesday after the encounter. If you're not feeling up to catching it, however, you can simply KO Red Gyarados. It's not gone forever; it will respawn once you get into the Hall Of Fame. And if you visit Lake of Rage on a Wednesday, the scripted shallow water effect will still be active. That way you retry this Shiny Pokemon encounter when you're better prepared, and with better weather.

Contributed by: discoinferno84 

Steven's Friendship

One of the optional sidequests you can do for Steven is trading Forretress for Beldum in Saffron City. When you obtain a Forretress, make sure to max out its friendship stat. After the trade is done, Steven will have some additional dialogue in which he remarks on the high friendship stat. He'll also comment how you must be a Steel type fan like he is, and gushes a little about why he likes them so much.

Contributed by: discoinferno84 

Sparkling Midnight Apricorns

Apricorn trees yield their fruit once a day. Normally, most players will simply grab their Apricorns whenever they happen to play. However, there is a surprise for those who harvest them at a specific time. Harvest them as usual, and then come back to the trees right before midnight. As the clock goes into the next day, the fruit will automatically regrow, and there will be a very brief animation in which the Apricorns sparkle.

Contributed by: discoinferno84 

Battle Hall fans - part 2

There is also an NPC, which changes depending on the player character's gender, that has different bits of dialogue and moves closer to the lobby where you sign up for battles depending on the number of species you've won at least one battle with in the Hall; these NPCs are called Serena if player character is male and Winston if player character is female, and they become more of a fan of the player the more the species of Pokémon the player wins a battle with.

The thresholds for different dialogue (and changes in position) are the following:

Contributed by: Andrex_93 

Mic Test (DS Models Only)

On the title screen, press X, Y, Down at the same time. This will activate the game's Mic Test for the Nintendo 3DS. This works on both HeartGold and SoulSilver Versions.

Contributed by: discoinferno84 

Unlockable Pokewalker Maps

There are over 20 Pokewalker maps currently available to anyone and everyone who owns them. The trick is obtaining Watts and getting the National Dex. Note that some of the following are event-only, so the Yellow Forest (for example), is unattainable right now.

Contributed by: marioman1154 

Dual Slot Pal Park Items (DS Models Only)

After you've unlocked Pal Park, talk to the Lady in the lobby. You can get special backdrops/accessories if you have a Pokemon GBA cartridge inserted into the DS before starting the game. The item you get is determined by which GBA you have. Each gift can only be given once, and you have to leave/re-enter Pal Park in order to receive a different gift from another cartridge. Note that this works for both HeartGold and SoulSilver Versions.

Contributed by: discoinferno84 

Pokedex Diplomas

Meet the conditions below, then speak with the Game Freak director in Celadon City to get the following diplomas.

Note that Mew, Celebi, Jirachi, Deoxys, Shaymin, Darkrai, Manaphy, Phione, and Arceus do not count towards this, and are thus not needed.

Contributed by: Anonymous 

Battle Hall fans

In the Battle Hall facility, it's possible to gain fans as the total record of wins (a.k.a, the combination of the highest win streaks with each Pokémon species) increases: depending on the number of wins and the gender of the player character, different NPCs will show up in the lobby, with different bits of dialogue.

Contributed by: Andrex_93 

National Dex

Contributed by: raytan7585 

Trainer Card Stars

By completing certain tasks in the game, you get stars added to your Trainer Card. (Of special note are the Shiny Leaves, found only by speaking with your Pokemon in certain areas on very rare occasions, the locations being Nature-dependent.)

Contributed by: Anonymous 

Unlock 8 bit music

Once you obtain all 16 badges, talk to the music designer in Celadon, and you unlock the 8-bit originals from the original gold/silver games.

Contributed by: big_one12 

Pomeg Berry Glitch

For this glitch to work properly, you must have a Pomeg Berry and a Pokemon who has not had their HP lowered as much as possible already through Pomeg Berries. (If the latter is the case, the use of HP Ups on the Pokemon will suffice.) Get the Pokemon to a severely low level of HP (1 or 2 HP). Once you do so, in the field, use the Pomeg Berry on the Pokemon. This will in turn cause the data in their HP to cycle back to the top of the counter, giving the affected Pokemon 65,535 HP - over 90 times the otherwise possible maximum in the game.

Contributed by: Anonymous 

Level Up Unhatched Pokemon

To do this glitch, you must first execute the Pomeg Berry Glitch, which is done by using a Pomeg Berry on a Pokemon with 1 or 2 HP so that its HP loops to 65,535 (displayed as ?35 in-game). Do so, however, with only one Pokemon and an Egg in the party, with the Egg in the top-leftmost slot of the party in the Pokemon menu. After executing the glitch, you will now be able to enter battles and use the Pokemon Egg as if it were a normal Pokemon. It will function as a normal Pokemon - you can view the stats it will have upon hatching, it can level-up by beating Pokemon, it can learn new moves, it can even evolve. This means that you can alter the Pokemon inside the Egg in otherwise-illegitimate ways. For example. Pikachu cannot normally know Thunder when hatching from an Egg at Level 5; through this glitch, Pikachu can. Similarly, you can hatch Eggs with fully-evolved Pokemon such as Typhlosion, Meganium, and so on, inside.

Contributed by: Anonymous 

Diamond Dust

On the following days, Fly up to Mt. Silver and instead of your usual snowfall, there will be glittery diamond snow:

February 29th (leap year day)
March 15th (Ides of March / Honen Matsuri)
October 10th (release of Pokemon Blue in Japan)
December 31st (New Year's Eve)

Contributed by: Anonymous 

Unlockable Pokewalker Routes

With regular usage of the Pokewalker included with SoulSilver, you can obtain Watts that can be used to unlock special courses that hold unobtainable pokemon in both HeartGold and SoulSilver versions. Watts are not total obtained, but collected in the game after returning from a stroll or sending gifts back to your game. There are also several routes unlocked by Nintendo Wifi Events and specific pokemon.

Contributed by: PersianGato 

Pokedex Diplomas

Meet the conditions below, then speak with the Game Freak director in Celadon City to get the following diplomas.

Note that Mew, Celebi, Jirachi, Deoxys, Shaymin, Darkrai, Manaphy, Phione, and Arceus do not count towards this, and are thus not needed.

Contributed by: Anonymous 

National Dex

Contributed by: raytan7585 

Trainer Card Stars

By completing certain tasks in the game, you get stars added to your Trainer Card. (Of special note are the Shiny Leaves, found only by speaking with your Pokemon in certain areas on very rare occasions, the locations being Nature-dependent.)

Contributed by: Anonymous