Let's see, where to start, where to start...
For most questions, go to the HG/SS walkthrough on the main site.
Entei&Raikou: Completely random in the Johto Region
Latios: Roaming the Kanto Region
Groudon: Embedded Tower, near the Safari Zone in the Johto Region
Suicune: Did you do the necessary means to see him where Misty was standing before you got her to go back to the gym? (For more info, go see the walkthrough)
You also can get the three legendary birds.
Articuno is in the Seafoam Islands, just like in Gen. I and Gen. III
Zapdos is outside the Power Plant.
Moltres is in the heart of Mt. Silver.
Mewtwo: Back in Cerulean Cave
Lugia: Whirl Islands after you get the Tidal Bell from the Kimono Girls. (You should already have the Silver Wing)
Ho-oh: Go to Pewter City and talk to the old man near the route that takes you to Mt. Moon. He'll give you the Rainbow Wing. With that, go to Ecruteak City and go into the Tower where the monks are blocking the stairs. The monk will stand clear to give you access. Good luck with the obstacles that await you!
More things:
Go to Saffron City and go into the Sliph Co. Building. Steven will be there, and he'll make you choose between the Red, Green, and Blue stones. Red one gets you , the blue one gets you , and the green one gets you . Also, if you have the Enigma Stone, then go to Pewter City and into the museum. There you find Steven (again!) and he'll be surprised that you have the stone and he'll extract the Soul Dew from it. Then he'll go outside and you'll see Latias waiting there. If you faint her, then she'll come back the next time you are there.
The Red Orb can be obtained by talking to Elm (I think).
Rayquaza: After you get a friend to trade you a legit HG (transferred ones don't count) Kyogre, go and take your Groudon and Kyogre to Mr. Pokemon (the one who gave you the Togepi egg) and he'll give you the Jade Orb. Go back to the Embedded Tower, and Rayquaza will be where you see Groudon.
Regis: Transfer/Trade from Platinum
Heatran: Trade
Other 4th Gen. Legendaries: Trade
Exceptions: , , and
You need a legit event Arceus (too bad the event ended a long time ago) and take it to the Sinjoh Ruins (For more info, check the walkthrough, as I'm not sure what to do from here)
Hope I helped!
~torchie13125
(I hope you find mine more informative)

Was this Mew pal park'd from a Gen III game, or was it from a Gen IV event? If it was a Gen IV event, then it is impossible to be shiny; if I recall correctly, Wonder Card/Mystery Gift Pokemon have a special method of personality value generation - the personality value is regenerated until it isn't shiny.

Can you post the level obtained, the location data, if it was an event Pokemon, the ribbons, the Original Trainer and the ID number? It would be easier to check if it was hacked.

Ok, this has happened to me twice now, I hatched a Nincada with Bug Buzz and Silver Wind, and when I level it up to 20 with a spot in my party open, and plenty of Pokeballs. I evolve it to Ninjask, however, no Shedinja appears in my party. Any ideas as to what could be going on here?

You know, I had thought that may be the issue...I didn't think that I had a Pokeball before when I got my shedinja. But I could have...thanks, I'll try that!

The Safari Zone guide on both Psypokes and Bulbapedia tell me that the Safari Zone blocks will upgrade after a certain amount of days the area has been "in use". What constitutes "in use"? Do I need to spend 500P and go into the SZ every day, or will it upgrade passively (without me having to visit)? This is a confusing point for me and not at all obvious if you think about it.

So I was recently looking through the psydex. Namely at Scyther and Scizor, and the level-up moves for Scizor says it learns bullet punch at lvl1. So does that mean as soon as Scyther gets traded and it evolves it tries to learn bullet punch?

And, before I forget, I am looking for someone who doesn't mind helping me out and trade-evolving some pokemon, I'm looking to evolve one of my Scythers, a Graveler, and an Onix, maybe even a Haunter. This also reminds me, does anyone know where I can get a magmarizer? I'm raising a Magmar and considering evolving it as well. While I'm basically asking/advertising all the trades I'm looking for, I may as well say that I'm also looking for a baby Charmander too, I'm not looking for any specific movepools or anything like that, I just ask that it not be filled with Hms when I get it. Baby Cyndaquil would be cool to get too, and Bulbasaur, even Torchic. That's all I can really think of right now.

No worries, it's never really specific on most dex's but yeah it has to be the actual poke ball. Hope it works out for you, always nice to get 2 pokemon for one.

So on what day(s) does red appear on Mt. Sliver after you beat him?

Thanks for the answer. But now I've got another question, possibly quite dumb and n00bish of me. But it never hurts to ask anyway. EXP share raising a pokemon in the back of my team deprives it of EVs right? Which is just as bad as Rare Candies, no?

I was wondering something when I was battling Lugia this evening. After I started barraging it with pokeballs I wondered, can you get the dark Lugia on HG/SS? The one from Pokemon XD ?

In Soul Silver.. where is a "moss rock" or wherever I need to go to evolve my Eevee into a Leafeon..?