🕯️1. Nang Mai (นางไม้) - Nymph

According to the Royal Institute Dictionary, B.E. 2554 (2011), the term Nang Mai (นางไม้) is defined as: "A female ghost believed to inhabit large trees, especially the Takian tree."

 No one can see the palace it has built in the tree, and if someone cuts it down, they will be cursed, sickly, or possibly go insane. In paintings, novels, and folklore, Nang Mai are typically imagined as beautiful young women with long hair, dressed in traditional Thai clothing—wearing a sabai / sbai (draped shawl) and chong kraben or pleated wrap-around skirt. They are believed to inhabit trees of significant size but not excessively huge ones. In many places, villagers tie three-colored cloths around trees after someone reports seeing a Nang Mai appear there.

In Thai tradition, there are both benevolent and malevolent Nang Mai. The benevolent ones often appear in beautiful forms to warn humans of dangers, while the malevolent ones may seduce men, take them as husbands, or even kill them. There are many types of Nang Mai, such as Nang Takhian and Nang Tani. 

(In the EP4 Reaction video, FirstOne also said that “She’s actually not evil, right?”. As mentioned above, there are two kinds of Nang mai so he was confirming that said Nang Mai was originally benevolent but turned evil because of Ramphueng)

Nang Tani and Nang Takhian are also regarded as Nang Mai, although a person who commits suicide and their spirit becomes trapped in that tree is not regarded as a Nang Mai.

The Nang Takhian version of Nang mai or Nang mai who inhabits a large tree is considered to be one of the most hostile Nang mai because they believe that the larger the tree, the older and more haunting it is. Some people also say that the more sap the tree produces, the more haunting the Nang mai who live in it are.

[1][2][3] 

A large Takhian tree - it took 7 people to be able to circle it - 📷: ภาพ/ข่าว ปัณณวิชญ์ พะเยา/ศูนย์ข่าวภาคเหนือ (via Thai independent news agency)

🕯️2. The 3 students’ punishments - observe the Eight Precepts for life

The Eight Precepts of life are [4]:

Refrain from killing living beings.

Refrain from stealing.

Refrain from all sexual activity.

Refrain from false or harmful speech.

Refrain from intoxicating drinks or drugs.

Refrain from eating after midday.

Refrain from entertainment, singing, dancing, music, and using perfumes or cosmetics.

Refrain from using luxurious seats or beds.

It is said to be observed by laypeople during intensive meditation periods or on the Uposatha Day (the full moon and new moon days) [5]. It is unclear if the 3 students will have to observe them on the Uposatha Day only or daily for the rest of their life. 

🕯️3. Suicide - Cannot be reincarnated as humans

Buddhism considers the root of killing rather than just its form, and it determines whether or not it is morally wrong based on a variety of complex and contextual elements. Suicide is viewed negatively by Buddhists since the first precept forbids destroying life, including one's own self; therefore, it is subject to the same moral standards as other forms of murder. When someone commits suicide out of rage, their final thoughts may cause them to reincarnate in a world of sadness.

We could only find information about the consequences of suicide, but none of that mentions not being able to reincarnate as humans (as Ramphueng implied, I think it's just one of the possible outcomes):

Buddhism recognises thought processes as rapid successions of thought after thought, and that the last thought of this life is the first thought and beginning of the next life. Since a person who is committing suicide is always associated with some degree of depression, misery, sadness, sorrow, hatred, anger, or pain, death by suicide will almost certainly lead to rebirth in lower realms of misery with possibly even greater sufferings, which counter the path towards enlightenment.

Those who end their own lives thinking that doing so would solve their problems, will in fact be born again and they will continue to suffer perhaps in more severe conditions.

[6][7][8]

🕯️4. The food offered to the dead cannot be eaten by the living

We cannot find more information about this belief. In Vietnam, food offered to our ancestors can still be eaten. However in this blog post of a man attending the Boon Khao Sak (บุญข้าวสาก) in Isan with his wife, he mentioned how the villagers would wrapped up the offered food for their family spirits and would place them in the “sugar cane fields, rice paddies, and other lands to feed the spirits (ghosts) that inhabit them” later. The villagers were said to go back and eat the leftover food from the offerings to the Monks.[9]

moonfordmdboy (Twitter), translated by ursdiorjk [10] stated:

“The living should not eat food that was intentionally prepared for the deceased, as it is considered an offering to the dead. Eating it oneself is seen as taking away the merit or blessing meant for the deceased, which can make the original intention incomplete. When making merit for the dead, it must be done with a pure heart. If someone eats the food first, it shows impurity of intention, and the merit or blessing may be diminished.” [11]

🕯️5. The concept of merit (บุญ) & making merit (ทำบุญ)

Merit (บุญ)

Merit or bun (บุญ) comes from punya in Sanskrit and punna in Pali, means “a virtuous or meritorious act, good or virtuous works”, “merit, meritorious action, virtue” [12] [13]. Merit in Buddhism is the accumulation of positive kamma (karma) through virtuous thoughts, words, and actions carried out with sincerity and purity of intention [14].

Many Thai believe in rebirth, that the life you live now is shaped by your past life, and the life to come will be shaped by how you live today [15, p. 49]. Therefore, merit influence karma and becomes essential in two main ways:

(1) Securing a favorable rebirth blessed with happiness, prosperity, and wealth;

→ Some Isan villagers believed if merit outweighs demerit, the soul goes to heaven until merit is used up, after which rebirth on earth follows.

→ If both merit and demerit are present, a person may first endure hell until their demerit is expiated, then enjoy heaven before being reborn.

→ If it was a life full of sin, a person may be in hell or wander the earth as phii before they can be reborn. [16, p. 54]

(2) Creating a happy and virtuous state of mind in this life.

→ Reflecting the view that virtue and purity, while fragile and easily disturbed, are the best preventive against misfortune. [16, p. 54]

Merit is also helpful for magical power of shaman, as demonstrated by Paran performed “Heaven and Earth Worship Ritual” getting responds from the divine as gentle rainfalls in EP 3 and “An Invitation to the Devas” getting help from the deities and gods to temporarily defeat Ramphueng in EP 2. Paran is someone with a lot of merit.

The Buddha said:

"According to the seed that’s sown, So is the fruit ye reap therefrom, Doer of good evil gather good, Doer of evil, evil reaps. Sown is the seed, and thou shalt taste the fruit thereof." [17]

Making merit (ทำบุญ)

The Buddha first explained Three Grounds of Meritorious Deeds:

Generosity or Giving (dana): giving, sharing, or supporting others to ease suffering.

Precept or Moral Behavior Observance (sila): living ethically by keeping precepts, fostering good relationships, and avoiding harmful behavior.

Mental development (bhavana): training the mind and developing wisdom..

Later, these were expanded into the Ten Grounds of Merit-Making:

Generosity or Giving (Danamaya)

Sharing or Giving out Merit (Pattidanamaya): dedicating the merit of one’s good deeds to others.

Rejoicing in the Merits of Others (Pattanumodanamaya): expressing joy or saying sathu (*) when others do good.

(*) Sathu (สาธุ) is a word equivalent to "amen" in Christianity. It can be variously translated as "amen", "good", "yes "thank you", "I have received", "well done", "be it so" or "all shall be well" (from Wikipedia).

Observing precepts (Silamaya).

Humility or Reverence (Apacayanamaya): showing reverence toward individuals with (1) age; (2) virtues or qualifications; (3) royal or noble qualifications. Ex: parents, teachers, monks, elders, or leaders.

Rendering Righteous Endeavors or Services (Veyyavacaccamaya): helping with wholesome activities that benefit others and the community.

Mental Development  (Bhavanamaya): practicing meditation and developing wisdom for inner clarity and peace.

Listening to Dharma (Dharmassavanamaya): actively and intentionally listening.

Teaching Dharma (Dharmadesanamaya): being a positive example by embodying Dharma principles.

Correcting One’s Views(Ditthujukamaya): developing clear and realistic understanding of good and bad actions and their consequences.

[14] 

📷: Ian (via iamkohchang) [24]

Thai ways of making merits [14]

Daily: Offering alms to monks and novices during their morning rounds.

Occasional: Observing precepts, meditation, and making offerings on holy days such as Visakha Puja, Asalha Puja, Magha Puja, and during Buddhist Lent…

On Special Occasions: ⇨ Auspicious Occasions: Births, weddings, graduations, house moving,... Giving alms to monks or donating to temples, seeking blessings for health, happiness, and prosperity. ⇨ Inauspicious Occasions: Illness or death. Giving alms to monks or donating to temples, seeking blessings for recovery or aid the deceased’s journey towards a positive rebirth, especially on the 7th, 50th, and 100th days after death, funerals or cremations.

Making merit is the core of Thai culture as well as many ceremonies, rituals, rites, festivals, special occasions in Thailand, including the 12 Heet - as mentioned in EP 1 post, 12 traditional festivals or cultural practices followed each lunar month, reflecting Isan people’s belief in Buddhism, ancestors, and protective spirits [18, p.97 - 98]. Just by participating in these ceremonies, it is both making merit and sharing one’s merit, the merit multiplies [15, p. 50]. In the past, during rice production or when going to fish or find food in the forest, villagers considered not only their and their family consumption, but also the need to make merit to the community, relatives, friends, monks, those in need and supernatural beings.[15,  p. 52]

When making merit by bringing food and alms to the temple for the monks’ morning and midday meals on Buddhist holy days, the monks recite prayers before and after the meal. During their after-meal prayer, they ask the Buddha, Dharma, and Sangha to acknowledge the donors’ good deeds and invoke blessings upon said donors. In this case, the monks provide the donors with the opportunity to make and receive merit. Similarly, the monks’ daily alms round is a blessing for the people, an opportunity to make merit [15, p. 50]. In the Buddhist view, merit is made not by giving, but “`acquired' by the willingness of the monks to receive” and the monk “is capable of transferring some kind of spiritual grace to the giver” [16, p. 53]. 

Villagers Make Offering of Food for the Monks - 📷: Allen A Hale (via Allen's World) [9]

A son will be ordained as monk to accrue merit for his parents as a way to show their gratitude. Some believe “once a son has been ordained his parents will have the yellow robe as a means of ascending to heaven”. If he has not been ordained while his parents are alive, they might not have enough merit to go to heaven and have a better next life. [15, p. 51]

🕯️6. Khem shared the merit with his mom - อุทิศส่วนบุญกุศล

In the novel, Chapter 12: “Khem shared the merit with his mom by pouring water from the brass vessel onto the ground.”

In Buddhist countries, merit is believed to be transferable and “sustains living beings in the afterlife”. Therefore, people share merit to the deceased loved ones by giving and donating to the monastic community. The recipient of said merit can have the merit as their needed items in the next life, and the giver’s merit does not decrease.[19] A Buddhist libation is often a way to make merit and transfer merit in Thailand like kruat nam (กรวดน้ำ) [20, p. 43], whether pouring into a vessel or onto the ground [21].

After an act of merit, by pouring water on the earth, some Thai people believe they “transfer some of this merit to the dead, to the gods, to other humans [...] thereby calling upon the goddess of the earth, Nang Thoranee (*), to witness the act.” [16, p.52]

(*) This is Phra Mae Thorani - Thailand Mother Earth Goddess Paran was calling for help in EP 2.

🕯️7. Sacred rice - Young Pharan used it to chase the ghost away

Rice is essential to Thai culture. Rice has traditionally been considered one of the most essential items by Thai people because of their long-standing tight ties to agriculture and rice cultivation. Additionally, rice is considered a sacred offering that comes from Phra Mae Phosop (the Rice Goddess). 

Ancient Thai occult practices see sacred rice as a ritual element. It can be applied in a variety of ways based on the objective. For example, in the literary work Khun Chang Khun Phaen, when Khun Phaen cast a spell over Khun Chang's home, he utilized rice dyed with magical herbs as a ritual tool. After lighting candles for the spell on the fence or the veranda, he would throw the enchanted, herb-dyed rice onto the roof of the house, believing it would put the people inside into a deep sleep.

Purpose of the sacred rice: 

Throwing it at different locations to drive away evil spirits and misfortune. 

Carrying it to protect ourselves from misfortune and evil spirits.

Sprinkling it on the main pillars or corners of a new house brings auspiciousness to the dwelling.

[22][23]

Bonus: the ghost in EP 1 is phi pop (ผีปอบ).

From Zeya on Twitter because she is Thai and I think she covered everything:

"Thai children often grow up hearing this phrase from adults in the home when we are naughty, such as "If you are naughty, watch out, a ผีปอบ (Phi-phop) will come and eat your liver."😶 So ผีปอบ is a type of ghost that is part of Thai folk beliefs, especially in the Isan region. It's believed to be a ghost that eats raw meat and never gets enough. They will keep looking for prey and only eat the internal organs, such as the chickens or dogs that the villagers keep. It's believed that those who become a Phi phop are usually those who use spells. 🙏🕯️or black magic. When they are unable to keep the spells they have or they break the prohibitions by using the spells to do bad things, it causes the bad things to come back to them. So they become Phi phop // Our Khemjira and Dang almost had his liver eaten. My babyy 😭🙏"

🕯️8. Misc:

About Charn's ability

moonfordmdboy (Twitter)[11], translated by ursdiorjk [10]:

"Charnvit has a strong mind because he was born on a Wednesday night. In Thai belief, people born on Wednesday night are thought to be “not blinded by spirits” ( “ไม่โดนผีบังตา”/ mai don phi bang ta) (phi bang ta - explained in EP 2 post), meaning they are protected from spiritual interference. When walking into the forest, such people are like living compasses; they can navigate and find lost individuals. People who get lost in the forest are often said to be “led astray by forest spirits or local guardian spirits,” but those born on Wednesday night are believed to have protective power for themselves and others, enabling them to guide others to safety."

In the novel: Ascension Ritual (พิธีสวดส่งวิญญาณ)

In the novel, Chapter 9:

“Khemjira shook his teary face, his large eyes pleading as he looked at Por Kru’s face. “So, what should I do?” Paran lifted the enchanted pot to place it in front of him. “Take it and have the temple perform the Ascension Ritual (*) for her. Let her go where she belongs.” “

(*) Ascension Ritual (พิธีสวดส่งวิญญาณ) is a ritual to send the soul on earth to a better and higher plain of existence.

We were unable to find credible info on this and we don't know for sure if it's what Khem was doing here. Just note it in case anyone interested or have a source!