In heart gold you can get on of each region's starters after beating Red. He has charizard, blastoise and venasaur if you need them. My pokemon ranch is how you get mew, and in heart gold you can get many other legendary pokemon from Kanto, Hoen and Shinoh. You can see every starter pokemon in platinum by battleing trainers. Some legendary pokemon can only be obtained by special events, and some like celebi are imposible to get without cheats. (Don't use cheats, they are no fun.