You said you bred a shiny litten? Could I breed a shiny Rowlet if I have a Decidueye? I don’t know how to breed in general, but could you tell me? Thank you!

yes, in general you can breed a shiny Rowlet from a Decidueye, but unless the Decidueye is from a different region, the chance to get a shiny is very slim.

you should probably look up the Masuda Method (on Serebii for example) where they explain to you how it works and how the method increases your odds for a shiny (though I was using the method and the Litten took me over 1600 eggs). 

generally I would recommend trading for a Ditto from another region, then you don’t have to worry about that again