I'm not sure if Crystal is the same (it should be), but in Silver and Gold versions Unown can be found in the Ruins of Alph.
nothing happens
You cant catch Articuno in Pokemon Crystal, only in Blue, Red and Yellow. But i am not sure about that.
no.
You can only catch Zapdos in Crystal by cheating. otherwise it is not in the game
I wouldn't. I'd catch your stupidity.
you don't catch articuno in crystal but you can get one from red, blue or yellow.
catch it in the wild
you catch it at night
You cannot catch Mewtwo in Pokemon Crystal, but you can trade it from a Pokemon Red or Blue. Hope this helped :)
First, you have to find them, then, you have to battle them, then, you catch them.
you can get seals with the unknows
you cannot catch a Pokemon that is already owned by another trainer. you can only catch wild ones.