Why does 定 (dìng) disable the monsters' movement in the movie 捉妖记 (Monster Hunt)? In the movie 捉妖记 (zhuōyāojì), called Monster Hunt in English (Wikipedia, IMDB, Baidu, iQIYI), the movie's character 霍小岚 (Huòxiǎolán) attaches the Chinese hanzi

定 (dìng)

to the head of monsters, and this largely disables their movement.  It's used humorously in various scenes.


  


I'm wondering what is significant about the character 定 in particular.

Question: Why does 定 disable the monsters' movement in Monster Hunt?

Among the definitions at dict.cn for 定, we have "to set" and "to fix".  It's possible it's used as short for 固定, which has "immobilization" among its definitions.  Although, I'm just guessing here, and I feel like there is more to it, possibly even something historical.
I know the magic "定身法"(the body-immobilization magic) from the very famous TV show 《西游记》, in which the protagonist "孙悟空" uses it to immobilize monsters. The magic spell he uses is a single character "定". It went viral since then. Kids would joke around about it. 

Nowadays, almost every native speaker knows this magic, given that 《西游记》 is such a popular TV show as well as its book.