A mischief-maker is someone who causes trouble on purpose — a quarrel, a scare, a little mess that sets people against each other. It is not an accident, and it is not the same as being clumsy. Grown-ups often use it of a child who enjoys being naughty but is not truly cruel; you can use it of an adult too, though then it can sound a little old-fashioned, even a little fond. It is milder than troublemaker in many ears: a mischief-maker sounds as if they like the stir, not as if they want to wreck something. You will meet it in stories, in family talk, and in a teacher’s tired voice. You almost never hear it in law or in a serious report. Though actually, the same person can be called a mischief-maker at home and a troublemaker at work — the word you choose is about how dark the trouble feels, not about a different kind of act.