poliwag?
try a pokéball.... it might help.
there will be an event where you can catch arceus coming soon.
Pokémon Diamond, you can only catch Darkrai during limited time distribution events however you would only be downloading it into your game.
Reshiram.
You have to download the azure flute from mystery gift.
You catch the legendary Poke mon. In platinum you catch GUIRETEINA, in pearl you catch PALKIA, in dimond you catch DIALGA
Like Gastlys & stuff...
No, you cannot catch Rayquaza in Pokémon Black.
No, you cannot catch Bulbasaur in Pokémon Black.
Darkrai cannot be found in Pokémon Black 2 so you will have to trade for one or transfer it from a previous game.
Catch a Ditto and give the item to Ditto... I think....
No, you cannot catch Regirock in Pokémon Black however you can acquire it via migrating or trading. Additionally you will be able to trade for it from Pokémon Black 2 or Pokémon White 2.