>>40579251Depends. Gen VII is friendly enough (SOS chaining or grab yourself a foreign language ditto off GTS/anon here and breeding by Masuda method) If you want Gen VI there's chain fishing, poké radar and friend safari and then anything other is longer odds with fewer methods to reduce it (gen IV MM is less effective than Gen VII for example). Static legendaries in Gen IV can be soft reset hunted (save, encounter, reload if not shiny, repeat) starting Gen V the box legends and certain other introduced legendaries are locked to prevent shininess (usually unlocked by their next appearance, ygarde being an exception) but any other legendaries that appear in the Generation usually are unlocked. There's also the warp holes in USM, which can give you any normal pokémon as shiny or bring you to an UB/legendary which you can soft reset hunt for either.
