The alternate coloured(or shiny)"legend dogs"is an event you will recieve after you pre-book your tickets to Pokemon: Phantom Champion Z, Zoroark. When you get to the movie premiere(in japan)of this movie, you will be able to choose one of them, raikou, entei, or suicune. They will be shiny, and have moves they don't usually learn. And once you trade them to Pokemon Black & White, it will unlock Zoroark, witch you will battle and capture(hopefully). But Zoroark has a special ability that lets him turn into any pokemon, so you can only catch him as his actual self. Now, about Celebi, you will recieve this Pokemon once you arrive at the premiere(i dont know what the conditions to recieve this are) but when you trade this to Pokemon Black & White, you will talk to a man who will give you zorua.