well, you cant... simple as that
(if you don't know why, it's because its an "only" Pokemon. meaning it's the only one.)
Acually you can breed a couple i know u can breed rotom and u get a rotom
you can't breed your starter pokemon cauz they are like the legandary pokemoni
No legandary pokemon can't breed
use the Pokemon locator.
Tyranitar
giritina, palkia and dialga
in unova, about 7 legandary pokemon. in total, about 28.
platinum:arceus leafgreen:mewtwo silver:lugia emerald:rayquaza
use an action replay or gameshark to catch them all
counting cheats its 34 without cheats 22
Dialga, Giratina, Heatran, Mespirit, Uxie, Azelf, Regigigas, Rotom, Cresselia,
There is many legendaries in sapphire but there is one legendary Pokemon what isn't in ruby and it is KYOGRE check out www.serebii.net
Dewgong is a fine Pokemon, but is far from Legandary my friend. You can't compare it to Pokemon like e.g. Mewtwo, Lugia or Groudon.