There are a few mischievous kids in the class. The teacher has a headache.
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调皮鬼 sounds harsh literally (鬼 means ghost/devil) but in practice it is affectionate teasing reserved for children. The 鬼 suffix turns adjectives into person-nouns with a fond, exasperated tone: 小气鬼 (miser), 馋鬼 (glutton), 胆小鬼 (coward).
