that is an old term for the Skills the Pets have. Bad Skill refers to Fetch (Hound), Wish (Fairy), Hoard (Imp), & Boost Element (Slime). it also refers to Root, Slow, & Silence Skills of Trinkets.
I asked this question awhile ago, and finally figured it out with help from other players. hope you enjoy the thread where I was looking for answers, and found answers to questions I didn’t know I had!