The Ritual of Phli Kam for Nature Spirits
   The skills needed for this ritual to invite nature spirits to reside in an amulet were taught to Ajarn by Kruba Sitthi, who was in his 90’s at the time. This knowledge was then later honed through studying with a Kruba who was also highly skilled in these practices. Now, there are few who can do this, and there are none who can tie them to the bearers name and birth details.
   The ritual of Phli Kam invites natural spirits into an amulet, and the most powerful forms of this ritual involve three types of spirits: Phi Suea (Guardian Spirits), Ngueak (Water Spirits), and Yak (Giant/Asura Spirits).
Phi Suea: The guardian spirits of houses, forests, cities, temples, villages, and mountains. They act as protective deities overseeing a specific location. For example, Phrai Takian (Takian tree spirits), Phrai Tanee (banana tree spirits), and various tree nymphs fall under the category of Forest Guardian Spirits (Phi Suea Paa).

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Phi Ngueak: These are ancient water spirits, and are spiritual entities naturally formed from aquatic life, as well as the souls of those who died in the water. These spirits possess great power in enchanting and deceiving the human mind.

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Phi Yak: These are spiritual entities with long lifespans and immense spiritual power. They reside in the forests and on mountains and are believed to be the retinue of the Asura deities from the Giant clan. They possess tremendous power.

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   The secret arts for invoking these natural spirits differ for each type and are by no means easy. If performed incorrectly, the energy can backfire on the Ajarn, because these natural spirits possess immense spiritual power, and are at least 500 to 1,000 years old. When invoking these spirits into sacred amulets, only one spirit is housed per individual amulet, so every piece contains a completely different soul.
   Each type of spirit possesses different powers. Furthermore, once a spirit is successfully invited into an amulet, kata are chanted to fill it with latent and supplementary powers tailored to the specific nature of that invoked spirit. It seems that all of the spirits that Ajarn will be bringing into amulets are present near to the lake where he does the Frog ritual to remove old Karma, which is close to the Wat of the Kruba who honed his skills with this ritual.

Ajarn Apichai on Bespoke Magic

Any sacred object that has a name and date of birth inscribed within and blessed into it can be passed down to family members. This is especially the case if it is passed to their children or grandchildren, who will even receive increased power. This is because once the owner passes away, their spirit or soul—what is called their ‘khwan’ in Thailand (spiritual essence)— will remain with that sacred object.That amulet will then have a ‘2-in-1’ power after the death of the bearer, who will now empower the amulet further. 
   Prai items usually last between 10 and 50 years before the spirit either departs or becomes a higher form. With Nature spirits, if kept and praised correctly, they can be passed down the line for centuries.