Oh, it is a black mischief.
– Arthur Miller
The Crucible, Act 2. John Proctor is commenting to Elizabeth on the dark and sinister nature of the witch trials, which have got under way. The word "mischief" can be taken to refer to the behavior of the young girls making the allegations. But Proctor uses it in a broader since to convey his disagreement with the unjust and unfair conduct of the trials and those in positions of power. The mischievousness of the girls has mutated into something much more malevolent and dangerous. Proctor is using the metaphor of "black mischief" to describe the court as evil. In Act 3 when John himself is before the court he will accuse the Salem judges of having "black hearts," because they know that their condemnation and conviction of people as witches is a complete fraud.