Lugia and Ho-oh: Without a cheating device you must go to a Nintendo event where you have to pay to get in and pay to get the Mystic Ticket to get to those islands. There is no damn point in doing it.
Legendary dogs: When you beat the Elite Four one of them will appear on random grass routes in Kanto. Which one you see will depend on your starter. Charmander = Suicune, Bulbasaur = Entei and Squirtle = Raikou. Raikou is my favourite.
You might want to use your Master Ball to get the one you should be encountering because they keep runing away, even thoguh they never heal themselves after battle.
Johto starter: Trade the one you can get in Emerald to Fire Red. You choose the one you get in Emerald.
I'm finished here...
Special thanks to Yossy666 for the avatar and signature images.