Hidden Powers depend on IV's, meaning Houndoom in general doesn't have a set Hidden Power...but your Houndoom has a set Hidden power...best way is to test it against various types to at least find its type, but power is a lot of calcs that aren't worth it..If you dont like your HIdden Power on your Houndoom (like maybe it's a HP Dark and that's a waste) then either breed a new Houndour, or don't use HP