You can't catch a pokemon once it faint's, legendary pokemon appear only once.
...? I got a second chance with my azelf... What happened? Blew my second chance, though...
You don't have to restart your whole game, just get anotehr game and trade Uxie and Azelf...Trust me it works....I ko'd Azelf so I ave to migrate it from another pokemon game
Really you can't but if you KO'd Girantina, after you beat the game you get a second chance in the turn back cave but I wouldn't risk it I suggest using the master ball you got from Cyrus. But any other legends, once in a life time so good luck!
You can't... You have to make sure they do not faint. .
You will have to restart it all over...
It is impossible to catch Azelf and Uxie after fainting them. Legendaries only battle you once. A tip: Before battling a Legendary, you should save the game so you can turn off the power without losing your whole game.