How can you let azelf reappear?

i know what your talking about but i dont know which one but all three of them will show up after you save them and stop palkia or diaolga, but they will only show up once. so you have to catch them. they will each be at the one of the three lakes. i think azelf is at lake valor. they are hard to catch. i used master balls on all. yes i did cheat XP. so good luck.