Spell

A spell was a specific action which, when performed correctly, channeled supernatural energy that allowed the caster to achieve a fantastical result based on the composition of the casting. It was the most basic form of employing Magic by any individual, but was especially prominent to the likes of Witches, Warlocks, Wizards etc., who possessed the power and knowledge to cast spells of great power with little preparation. Spells allowed individuals to alter reality on certain levels, such as affecting the physical properties of objects and people, giving the caster access to supernatural powers and changing the very existence of reality itself.

Casting spells
Spells often consisted of the verbal recitation of text, an incantation, but some spells had other requirements, such as special objects, ingredients and physical actions, such as mediating on the floor. Spells also tend to involve the summoning of a Higher Being with the user pleading for them to do their bidding. Instructions for casting certain spells were recorded in books allowing other practitioners to learn how to perform them (such as the Writings of Dramius, Books of Ascension and Bynum's History of Witchcraft  ) while some practitioners recorded their own spells in their personal spell books. Specific languages were known to be used when chanting incantations. These usually included Latin-based phrases or words, though English, Romanian, ancient Sumerian and the demonic language of Pylean were also used in spells. The caster did not have to know the language for the spell to be successful, but pronouncing the words correctly were imperative. A powerful caster was capable of overcoming the limitations of language-based incantations, as shown with Willow Rosenberg who initially spoke the Latin incantations of a Portal Spell before changing to English when she decided to take charge and command the higher forces to open a portal, admitting to "suck at Latin".

Spells may not even have to be cast with intent as Xander Harris, who had no prior experience performing magic, accidentally set fire to a book after nonchalantly reading out an incantation from it, even though Willow claimed that spells needed the caster to have concentration and being "attuned with the forces of the universe". In a larger example, Willow unknowingly caused herself to be invisible to her friends and vice versa as she worried about how they would perceive her.

Particularly powerful spells needed the caster to have a considerably high level of experience and power to cast them successfully, as well as the right the tools. This could be due to the type of magic it involved or the god it invoked. For example, the Sacrifice to Osiris could not be performed without his urn, calling upon the goddess Thespia could only be done by practitioners of a high level, and in the portal spell Willow needed to drain some of Anya Jenkins' and Kennedy's life force in order to power it. Since magical energy factored in the casting of spells, spells that used a lot of dark energy were known to block the casting of lesser spells.

Identifying spells
All spells left a trace signature after they were cast which weren't perceptible to the human eye unless the ritual Tirer La Couverture was performed. This made the user enter a trance which showed them a before-and-after of the world affected by the spell that they intended to identify. Witches could also be identified if they cast a spell in the last 48 hours by combining some quicksliver (mercury), aqua fortis (nitric acid) and the witch's hair, heating it and applying it to the witch's skin, whereby on the second contact is made the witch's skin turns blue. This was used to identify Amy Madison as a witch (though at the time she switched bodies with her mother, implying that spells left an impression on the user's body rather than spirit). It's unknown if this worked on witches only or any type of practitioner.

Creating and modifying spells
The majority of existing spells were products of ancient societies (hence the use of foreign languages), though new spells could be created by using existing spells as a template, and tweaking the effects of those spells to best suit the caster. For example, Tara Maclay taught Willow how to create a "little tinkerbell light", only for Willow to have "tinkered with the Tinkerbell", allowing her to create enough light to uncover a dark hallway. Willow then attempted to modify this spell even further by trying to create a Simulated Sunlight spell, but was never successful in doing so. In another example, the Enochian protection runes could be utilized for a concealment spell that rendered the user unable to being detected by psychics and higher beings during the time it was created, but in modern times, the spell's effects were transposed for modern surveillance, such as security cameras. Also, when rebuilding his karaoke bar, Lorne organized a new Sanctorium Spell to prevent violence from both humans and demons in the bar, because in the original bar, the spell only prevented demon violence.

Countering and undoing spells
"Let the healing power begin. Let my will be safe again. As these words of peace are spoken, let this harmful spell… be broken."

- Willow reverses her own spell.

The effects of spell can be undone by a reversal spell which tended to act as the exact anti-thesis of the original spell, such undoing the effects of a Draconian Katra by conjuring a new one, or recalling the deity that was originally summoned in order to the cast first spell and asking them to undo it in the second. Practitioners could also reverse the effects of a spell manually by destroying tools that were essential in the continence of the spell, or by absorbing the caster's magical energy and decoding it into whatever the other person wanted it to do. It was also shown that some spells needed to be continuely fueled by magical energy in order for it to keep working. For example, following the loss of all magic in world, Dawn Summers started to revert back into the Key as the spell responsible for making her human did not have access to any magical energy. Certian spells were cast specifically so they could be broken by the victim (or a third party) if they performed a certain action. The Time Loop Spell could be modified so that those affected by it would repeat the task over and over until they completed it successfully, the Transformation Curse could only be broken if the victim learned their lesson as even a powerful witch like Willow admitted that she couldn't undo the spell herself (Serious magic is kinda like improve, Dawn. You can't stop it cold; you gotta adapt.), and the True Love spell put the victim in a permanent sleep until they were kissed by their true love. The Ritual of Restoration, the spell to restore a vampire's soul, was made with a flaw, not an intended countermeasure, whereupon the ensouled vampire could lose their lose if they experienced "perfect happiness".

Rituals
Rituals were spells that involved a combination of incantations, ingredients, objects and actions performed in an orderly fashion. Magical rituals had to be performed undisturbed for the spell to be successful. For example, when casting a spell, Willow was adamant that Anya not speak as any "non-ritual word" could have catastrophic results, which proved to be true when their erupting argument led to the conjuring of a troll. In another instance, when Willow and Anya botched their attempt at creating a temporal fold, because the visions caused by the spell made Willow shake so much that the sand that was meant be poured over the image of Anya's necklace, so that it could be extracted from an alternate reality, instead poured on Willow's leg, causing her counterpart in that reality to be summoned into theirs.

Rituals could include the additional presence of two or more individuals to aid in the casting of the spell, usually by reciting a particular verse to compliment a verse recited by another caster. Sometimes rituals required all participants to be actively involved (such as the Enjoining spell ) while others had one participant in charge of executing the spell with the other participants merely assisting them by doing simple tasks like chanting short incantations, waving burning sage or holding candles (for example, the Ritual of Restoration and the Sacrifice to Osiris ). Some rituals needed the participants to be positioned a certain way, usually in a circle with the components placed in the center. Symbols may also have to be used during rituals, such as pentagram drawn on the floor (used in the Dedication, the Demon Corporification Spell and in disfigurement spells ) Rituals were also known to have sartorial requirements, particularly robes. Xander was also once required to be shirtless and wear markings on his chest while holding a candle to cast a Love spell.

Thaumogenesis
Thaumogenesis was the process wherein the casting of a powerful spell resulted in the unwanted creation of being (usually a demon) to act as a side-effect or universal price for having the caster’s will done. Anya Jenkins compared the process to a “gift with purchase”.