Niffins are powerful beings that are pure magical energy, created when a Magician fails to maintain an emotionless mind while controlling a spell and becomes consumed by it.
It is a general rule by most magicians that niffins must be "boxed" on sight, as niffins have been noted to be incredibly dangerous. Most niffins can be trapped in specially made boxes, but certain niffins have been able to escape them. They possess similar immortality to that of Deities, as there are no known-methods of destruction or killing them. Niffins become greatly angered when they are summoned. Upon transforming, a magician loses their shade, which is why most rituals to restore them their humanity fail.
When a Magician is consumed by a spell, their body will begin to distort rapidly. If they continue to attempt casting, their hands will burst into blue flames, the spell will fail and the body will be burned into nonexistence. Once a magician becomes a niffin, they retain their original appearance, but their skin partly glows/burns with blue energy running through like blood in veins. During this transformation, the Magician loses their shade.
Products of a failed spell-casting in which either a magician continued to cast a spell but didn't not have enough power to actually complete the spell in the first place or a magician unable to maintain an emotionless mind while casting a spell. Niffins are largely an unknown and less studied entities due to various reason, what is known is limited.
As they aren't human any longer, most niffin are rather violent and deadly, described as a bloodlust. However, not all niffins have been attributed with this (e.g Alice), one insists that she doesn't feel the urge to kill anyone, but rather, she wants to be free to do whatever she wants and perform beautiful magic. Niffins can be contained like much like cacodemons, within a magician's body like a cage, but over time, the magician's body won't be able to hold a niffin for much longer and will eventually kill the holder. The power of a niffin has been compared to one of a god: Alice specifically allowed herself to become a niffin in order to kill the Beast and later express the capability to kill Reynard. Reynard claims that although a niffin would not be able to kill him. It's been claimed by a Niffin that they are able to perceive magic to a deeper and more profound degree than a Magician, and are able to perform more complex magic that does not require hand gestures. 
Those turned into a niffin display a vastly increased capability and ability for magic and all that it entails. The degree of increase is vast enough that a complicated unlocking spell that would've required a genius magician hours, was solved in 15 seconds. They are able to travel and teleport in blue smoke and fire. Alice's knowledge in the days she was free allowed her to understand many rules of magic, which allowed her to accurately predict that Ember's murder would result in the Old Gods shutting off Earth and Fillory's magic.
Alice once also sought out to reverse the niffin transformation and restore her brother to human. Quentin would later attempt the same with Alice and bring her back, but set her free briefly, until he was able to bring Alice's shade from the Underworld and restore her with it.
Niffins such as Friar Joseph who inhabit worlds devoid of magic are capable of dying.
"Boxing" a Niffin Edit
A special wooden box must be carved and be enchanted by a month long ritual. The box has no lid as the niffin becomes part of the wooden structure in itself, and therefore cannot be released. While boxing a niffin, a Turkish incantation must be said 3 times. This incantation is "Seni Bağlıyorum" or "Seni Bağlamak", both means "I bind you" in Turkish. (TV)
There have been incidences wherein a niffin is able to work around a "boxing" and escape.
Restoring a Niffin to Human Edit
It is possible to restore a Niffin back into a human but it requires 3 essential things for the spell to succeed:
- A power source, strong enough to fulfill the spell completely to its end
- The individual's Shade, who became a Niffin. Many spells specifically failed due to a lack of a shade
- A specially made metal cage to contain the niffin
The shade is put inside the cage and subsequently locked inside. The niffin called in towards the cage, drawn in by its shade. The power source to be used must be put into use and are suspended in place around the spell circle. upon the invocation of the spell with both the Shade and Niffin present, both forcibly combine, leaving a fully whole human in its place.
Those restored are equivocal to a new born in terms of magic and cannot cast magic as they would prior. They will also slowly lose all magical knowledge and insight towards magic that they might have learned during their days as a niffin, but have intact memory of their days as one.
- ↑ The Magicians (Television): Season 2, Episode 9