Mischief is playing harmless tricks on people or doing things you are not supposed to do. It can also refer to the desire to do this.
The little boy was a real handful. He was always up to mischief.
这个小男孩真是难管教。他总是在搞恶作剧。
Mischief is behaviour that is intended to cause trouble for people. It can also refer to the trouble that is caused.
The more sinister explanation is that he is about to make mischief in the Middle East again.
更为不详的解释是他又要在中东制造事端。