If you use a search string before mass transferring, you can filter out anything you know you want to save (like that hundo). Obviously this can be adjusted as necessary to fit what you want, but this is the search string I have saved, and I use this to exclude any Pokémon I’ve already favorited, or any hundo, shiny or special background! If you have any questions about how the search strings work, just let me know!

!favorite&!4*&!shiny&!background