Two shiny Pokémon breeding is the same as breeding without a shiny Pokémon. The only exception is the Masuda method. The Masuda method is when you breed two Pokémon that are from different languages. For example, Japanese and English. If you had a Japanese Ditto and English Frosslass, you have a much higher chance of hatching a shiny Snorunt. Note: this does not only work with a ditto. You could have the same situation but with a Glalie instead of Ditto Also, the chances are normal if the two countries speak the se language. For example one Pokémon from America and one from the UK will have normal rates for a shiny egg. But one from America and one from Germany for example will get the boosted chance.