Traditionally, Phi Phop is related to the 'mountain-wind' (蛊) sorcery which is similar to the Malay 'santau' incidentally speaking.
In Indochina, the 'mountain-wind' is a type of poison that can kill but in order to be effective, it must be carried by an agent. In this case; the Phi Phop.
Likewise in Malay magic, the 'santau' is transmitted through the 'hantu raya' (helper spirit).
In Thailand, Phi Phop is believed to attach itself to a wild banana plant and some Chinese believes Phi Phop to be identical to a banana spirit. But if we travel further to Indochina and Southern China, then Phi Phop is merely the spirit of deceased 'mountain-wind' sorcerer.
The appearance of Phi Phop that I know is almost similar to the 'hantu raya' but it is slimmer and more greenish in color.
I obtained my Phi Phop from a Thai sorcerer under the guidance of my Kurba Archan but I seldom evoke its service as yet.
Like the 'hantu raya', Phi Phop can be trained to unite with a practitioner's soul but in doing so, the practitioner will face the risk of becoming another Phi Phop himself/herself.
Through my experience dealing with Phi Phop, I believe that Phi Phop and the common belief banana spirit are two different entities altogether. Although at times Phi Phop can be found attached to a banana plant too.
In old Thai medicine, Phi Phop can be exorcised out from a person's body by applying chili powder into the possessed's eyes.This method however, is largely forsaken as it would bring harm to the patient as well.
Other method of curing illnesses caused by Phi Phop is through herbal medication and prayers.
According to old scriptures, there are many types of Phi Phops in Indochina. For example the most powerful one is the 'golden silk' and other varieties are: the snake,the toad, the catfish etc.
Although the mountain-wind sorcerer is monopolized by the Indochinese minorities, some Mao Shan Taoists also perform some sort of 'mountain-wind' ritual.
I have had some opportunities to witness the making of these Taoist 'mountain-wind' variety and found that their power is far lesser than the minorities ones.
This is because the Mao Shan people only makes 'poisons' but they didn't have the associated spirit to be the agent.
Now a days, such distinctions are not important any more because the masters of Phi Phops and the related Mao Shan practitioners are very hard to come by practically speaking.