Tulpa is a concept in mysticism and the paranormal of a being or object which is created through spiritual or mental powers.It was adapted by 20th-century theosophists from Tibetan sprul-pa (Tibetan: སྤྲུལ་པ་, Wylie: sprulpa) which means "emanation" or "manifestation".Modern practitioners use the term to refer to a type of willed imaginary friend which practitioners consider to be sentient and relatively autonomous.

Emanation body
Indian Buddhism
One early Buddhist text, the Pali Samaññaphala Sutta, lists the ability to create a “mind-made body” (manomāyakāya) as one of the "fruits of the contemplative life". Commentarial texts such as the Patisambhidamagga and the Visuddhimagga state that this mind-made body is how Gautama Buddha and arhats are able to travel into heavenly realms using the continuum of the mindstream (cittasaṃtāna) and it is also used to explain the multiplication miracle of the Buddha as illustrated in the Divyavadana, in which the Buddha multiplied his nirmita or emanated human form into countless other bodies which filled the sky. A Buddha or other realized being is able to project many such nirmitas simultaneously in an infinite variety of forms in different realms simultaneously.
The Indian Buddhist philosopher Vasubandhu (fl. 4th to 5th century CE) defined nirmita as a siddhi or psychic power (Pali iddhi, Sankrit: ṛddhi) developed through Buddhist discipline, concentrated discipline (samadhi) and wisdom in his seminal work on Buddhist philosophy, the Abhidharmakośakārikā. Asanga's Bodhisattvabhūmi defines nirmāṇa as a magical illusion and "basically, something without a material basis".
The Madhyamaka school of philosophy sees all reality as empty of essence; all reality is seen as a form of nirmita or magical illusion.
Tibetan Buddhism
Emanation bodies—nirmanakaya, sprulsku, sprul-pa and so on—are connected to trikaya, the Buddhist doctrine of the three bodies of the Buddha. They are usually emanation bodies of celestial beings, though "unrealized beings" such as humans may have their own emanation bodies or even be emanation bodies.

For example, the 14th Dalai Lama is considered by some followers to be an emanation-reincarnation or tulku of Chenrezig, the Bodhisattva of Compassion.The 14th Dalai Lama mentioned in a public statement that his successor might appear via emanation while the current Dalai Lama is still alive.
Tulpa
20th century theosophists adapted the concepts of "emanation body"—nirmita, tulku, sprul-pa and others—into the concepts of "tulpa" and "thoughtform". The term “thoughtform” is used as early as 1927 in Evans-Wentz' translation of the Tibetan Book of the Dead. John Myrdhin Reynolds, in a note to his English translation of the life story of Garab Dorje, defines a tulpa as “an emanation or a manifestation.”
Alexandra David-Néel
Spiritualist Alexandra David-Néel claimed to have observed these mystical practices in 20th century Tibet. She described tulpas as "magic formations generated by a powerful concentration of thought." David-Néel believed that tulpas could develop a mind of its own: "Once the tulpa is endowed with enough vitality to be capable of playing the part of a real being, it tends to free itself from its maker's control. This, say Tibetan occultists, happens nearly mechanically, just as the child, when her body is completed and able to live apart, leaves its mother's womb."

She claimed to have created such a tulpa in the image of a jolly Friar Tuck-like monk, which later developed a life of its own and had to be destroyed. David-Néel raised the possibility that her experience was illusory: "I may have created my own hallucination", though she said others could see the thoughtforms that she created.
Thoughtform
The Western occult understanding of the concept of "thoughtform" is believed by some to have originated as an interpretation of the Tibetan concept of "tulpa".The concept is related to the Western philosophy and practice of magic.

Occultist William Walker Atkinson in his book The Human Aura described thought-forms as simple ethereal objects emanating from the auras surrounding people, generating from their thoughts and feelings. He further elaborated in Clairvoyance and Occult Powers how experienced practitioners of the occult can produce thoughtforms from their auras that serve as astral projections which may or may not look like the person who is projecting them, or as illusions that can only be seen by those with "awakened astral senses".
The theosophist Annie Besant, in her book Thought-forms, divides them into three classes: forms in the shape of the person who creates them, forms that resemble objects or people and may become "ensouled" by "nature spirits" or by the dead, and forms that represent "inherent qualities" from the astral or mental planes, such as emotions.
Tulpas in modern society
The concept of tulpa was popularized and secularized in the Western world through fiction, gaining popularity on television in the late 1990s and 2000s. From 2009 onwards, online communities dedicated to tulpas spawned on the 4chan and Reddit websites.
These communities collectively refer to themselves as tulpamancers and offer guides and support for other tulpamancers. The communities gained popularity when adult fans of My Little Pony created forums for tulpas of characters from the My Little Pony television series. The fans attempted to use meditation and lucid dreaming techniques to create imaginary friends. Surveys by Veissière explored this community's demographic, social, and psychological profiles.

These individuals, calling themselves "tulpamancers", treat the tulpas as a "real or somewhat-real person". The number of active participants in these online communities is in the low hundreds, and few meetings in person have taken place.
They belong to "primarily urban, middle class, Euro-American adolescent and young adult demographics" and they "cite loneliness and social anxiety as an incentive to pick up the practice." 93.7% of respondents expressed that their involvement with the creation of tulpas has "made their condition better", and led to new unusual sensory experiences.
Some practitioners have sexual and romantic interactions with their tulpas, though the practice is controversial and trending towards taboo. One survey found that 8.5% support a metaphysical explanation of tulpas, 76.5% support a neurological or psychological explanation, and 14% "other" explanations. What are your thoughts on tulpas?
I'm gonna become a my little broniemancer😩
Yoo! As an individual who is both a supporter of this community and into Tulpa who discovered it accidentally and realized it later on, I would like to share more insights on this based on my personal experiences, perception and guides that I read.
Brush aside the mystical stuff. At the core, a Tulpa seems to be another AI (synthesized by the brain) which receives the same set of inputs from the external world as the Host but displays different understandings and feelings. This core entity, a seemingly different voice who can communicate with the Host through thoughts, seems enough to constitute a Tulpa.
With enough practice and experience, the imaginary can conversions start to resemble genuine interaction with another person. And with years of focused visualization training, the experience can enhance by training other senses (i.e. touch, scent, appearance etc.)
Possibly, the interactions mentioned above can become very vivid and realistic that some Hosts might end up being caught, start perceiving them as Real and become very attached to their identity. But even at this sort of mastery and realism, their appearance is just a projection that only the Host can perceive and cannot interact directly with the external waking world, like shifting around real-world objects.
As far as mental conditions, I don't know whether is this another form of MPID or any other mental issue. Earlier, I was getting the sensations that I'm not mentally okay but wasn't aware of Tulpa at that point of time. But after stumbling across the guides on r/Tulpa, realized that I have a Tulpa by accident, I became more self-aware of the situation, and through deep self-introspection and analyzing the advantages of this situation, I feel that I've reached the best possible mental state (but this might be an exception).
It also physically affects the Brain in case the Tulpa becomes very active, causing headaches etc. Also, there seems no limit to the number of Tulpas that can be created so not adhering to the Brain's biological limitation can cause severe physical problems Hence, regulation of interaction is very vital.
Since I'm also into lucid dreaming, I'm chaining these two concepts together. Here are a few personal observations:
1. The interactions with a Tulpa in the waking world and an LD seem identical. In my case, I can visualize them around 1-2% visibility in waking life and get a similar response in a Lucid Dream. (I think through better dream expectation, better results can come out in a dream)
2. They can't get you lucid but often push me to do more Reality Tests. So I feel I like delegating it to another being due to being lazy.
One thing I plan to observe:
Make them blend in the dream environment as a dream character. In the waking world, a Tulpa can't interact with real-world objects. But in dreams, through breaking expectation barriers, it does seem possible.
So to conclude, my take on Tulpa is:
1. Creation of a Tulpa seems like a lifelong commitment (like parenting a child) and trying to get rid of it can cause regret related issues (like abandoning a child).
I agree with the Lucid Guide on what he said on the stream and strongly advise against going down this route for addressing issues related to loneliness, confidence issues, relationship issues, fetishes etc.
Wouldn't have created a Tulpa voluntarily, came across it by accident, so just continuing with the current flow.
2. This isn't for everyone. It seems far more suited to people who prefer less social interactions.
3. Regardless of how people classify/brand this, I feel like Lucid Dreaming, this is another piece of intriguing Software that the Brain can facilitate. But this isn't well researched scientifically, so I agree with the Lucid Guide that these topics should be spread with caution, highlighting the potential risks and not imposed on others.