Nàge suǒwèi de dàshī jiùshì zài zhuāngshénnòngguǐ piàn qián.
That so-called master is just playing supernatural tricks to scam money.
Tips
history
Recorded in Cao Xueqin's 《红楼梦》 (Dream of the Red Chamber), ch. 37: 你们别和我装神弄鬼的,什么事我不知道? - 'Don't try to pull spooky tricks on me; what is there I don't already know?' The chengyu has carried that scornful tone ever since.
memory
Literal: 装 'pretend to be' + 神 'gods' + 弄 'play with' + 鬼 'ghosts'. Picture a fake shaman hamming up a séance - exactly the image the idiom evokes.