no, you don't have to but I did just for completing the dex
uxie azelf dialga, mespirite, girantina and heetran
You can catch Dialga, Uxie, Azelf, and Mesprit
Dialga, Giratina, Heatran, Mespirit, Uxie, Azelf, Regigigas, Rotom, Cresselia,
You can't, you will need to trade them from Pokemon Diamond, Pearl or Platinum.
In Pokemon diamond you can catch Dialga, Azelf, Uxie, Mesprit, Cresselia and Arceus
You will need to catch the three lake lengendary pokemon. (Mesprit, Uxie, Azelf).
Dialga, Uxie, Mesprit, Azelf, and probly Arceas.
sorry man, but you cant get a azelf uxie or mesprit in Pokemon soul silver...
no you cannot
Without trading, cheating, or Nintendo events, you can get Dialga, Uxie, Azelf, Mesprit, Heatran, Giratina, and Cresselia.
you can go back and catch: -azelf -Uxie -Mesprit and also a SECOND -Palkia and a SECOND -Dialga
they are mespirt, azelf, uxie, and dialga