come and go like a shadow 神出鬼没

“神出鬼没”，汉语成语，像神鬼那样出没无常。原指用兵灵活机动，今多比喻行动变化迅速，出没无常，不可捉摸。可以翻译为“come and go like a shadow，appear and disappear mysteriously”等。

例句：

游击队神出鬼没，搞得敌人晕头转向。

The guerrillas came and went mysteriously, driving the enemy out of their wits.

他神出鬼没，不知一天都在干什么。

He is a mysterious person; no one really knows what he is doing from day to day.