while witches between Supernatural and the Vampire Diaries display similar powers, there is a biological difference among them. No offical name has been given to either type, though the term "True witch" has been used to describe Vampire Diaries witches.
Supernatural
A witch is a human who has gained magical powers through the practice of witchcraft. Both men and women can be witches. Any human can preform witchcraft, but only those who strive to become witches will gain the powers.
Vampire Diaries
Witches are supernatural beings with the power to affect change by magical means by connecting with various sources of magic.
Powers
Both types of witches display similar powers such as;
Spell Casting
Potion Brewing
Elemental Control
Channeling
Telekinesis
Biokinesis
However, Vampire Diaries witches tend to also be psychic in varying degrees.
Depending on the witch, they can have more, or less powers than another. Also depending on the witch, and where they gain their power, individual power levels will vary.
Power Sources
While some witches can use their own energy for their power, it's not regarded as a stable or safe source. Because of this, witches often gain power from other sources.
Supernatural
Supernatural witches tend to gain their power from malevolent sources such as demons. In return, they sell their soul to the demons to be able to draw from their energy. However, not all witches rely on demons, some even claim to have nothing to do with them. Witches who do source their power from demons are generally stronger.
Vampire Diaries
Witches from The Vampire Diaries have multiple forms of sources.
Ancestral Magic
Ancestral Magic is a form of sorcery commonly used among the witches of New Orleans. This magic is highly dependent on a cyclic ceremony called the Harvest. The Harvest is a magic ritual which occurs once every three centuries involving the sacrifice of four young witches.
Dark Magic
Dark Magic (or Black Magic) is a form of sorcery that draws on malevolent powers, and may be used for negative purposes (e.g. to cause destruction or misfortune, to injure or kill, or for the profit of oneself rather than for the benefit of others.) In popular usage, the term "dark magic" is often used to describe any form of sorcery that is used negatively.
Expression
Expression is an extremely dark form of magic that draws on darkness that doesn't exist on the natural plane without harming it. The details and history of expression remain unknown, however according to Nandi, the forces of expression are considered so powerful that many witches discredit it as magic, for it expands beyond the limitations of both traditional and contemporary forms of witchcraft.
Sacrificial Magic
Sacrificial Magic is a form of witchcraft that draws power from killing offerings and making the witch stronger. Sacrificing supernatural beings generates more power than the sacrifice of humans.
Spirit Magic
Spirit Magic draws on the power of the Spirits of Nature and dead witches, and may be used for either good or evil purposes. Unlike other forms of magic, a witch can only use Spirit Magic however the spirits see fit. If a witch abuses the magic bestowed upon them, the spirits may break the connection, preventing the witch from harnessing their power. Bonnie Bennett once channeled the energy of one hundred dead witches in her attempt to kill Klaus. However, after she used the power to resurrect her dead boyfriend, the spirits declined Bonnie from further channeling them, as they viewed resurrection spells as a violation against nature.
Traditional Magic
Traditional Magic is the most common form of witchcraft among modern witches. Traditional Magic draws energy from the forces of Nature and may be used however the witch sees fit. Although Traditional Magic is very popular among the witchcraft community, it also very exhausting. Due to the fact the witch is exerting their own energy, the witch may experience symptoms of dizziness, fatigue, and minor nose bleeds. Bonnie Bennett explained the limits of this power to Jeremy Gilbert, saying that if she pushed too hard, it would push back.
Traveller
Traveller Magic is a form of witchcraft used by a sub-culture of witches known as the Travellers. According to a witch called Mia, this magic works differently from Traditional Magic and leaves the practitioner unable to perform Traditional Magic. This form of magic specializes in spirit possession and it's spells are cast in a language different from all other forms of witchcraft.
Tools
Both types of witches appear to use similar tools for witchcraft. They include;
Candles: Materials used to amplify a witch’s spell.
Grimoires: A family journal documented with ancient recipes, rituals, and spells.
Herbs and Stones: Materials used as ingredients for brewing and concocting paranormal potions.
Talismans: Materials used to amplify a witch’s powers.
Supernatural witches also tend to use hex bags, enchanted coins, enchanted cards and other items to direct curses and specific spells onto a particular person.
Weaknesses
Weaknesses seems to be another major difference point between the two types of witches.
The Vampire Diaries
Disbelief: The act of denying or disbelieving in ones magical potential could cause a witch to inadvertently suppress their paranormal power.
Fear: A distressing emotion aroused by impending danger, evil, pain, etc., whether the threat is real or imagined; the condition or feeling of being afraid could cause a witch to temporarily lose their powers.
Mortality: They share many of the same weaknesses as non-supernatural beings (e.g. age, decapitation, disease, heart-failure, suffocation, etc.)
Overuse of Magic: The excessive use of magic could lead to disorientation, nose bleeds, unconsciousness, and if taken to the extreme, death.
Supernatural
Despite their great powers, witches are still mortal humans, and can die just as easily as them, unless they use magic to enhance or protect themselves.
Iron - It appears that some, of if not all, of a witch's powers can be blocked with iron, as James couldn't astral project until his iron chains were removed. Likewise, he most likely couldn't use magic to escape, as he asked Dean and Sam to remove the iron chains. However, this may just be because most witches draw powers from malevolent sources such as demons and spirits which are weakened against iron.
Witch Killing Spell - A spell that once prepared, it kills any witch it hits, and makes it impossible for them to use magic to protect themselves. It has a very small range, as it killed one witch but left another who was standing only a few feet away unharmed. (Has not be confirmed to work on Vampire Diaries witches)
Devil's Traps - Devil's Traps seem to affect certain witches (The Wicked Witch was burned when she tried to cross one).
Biological Difference
It's clear the two types of witches are two different species, however to unknowing persons, they seem and appear the same.
The biggest difference between the two is that Supernatural witches have longevity--Some are well over 500 years old and appear to be within a range of 20-40 years old. However, considering the only witches seen with these lifespans were clearly stronger than normal Supernatural witches, and as such, could have made further deals with demons to extend their lifetime or simply draw on the demon's energy to create spells that make them live longer. A pair of witches were also known to take years from humans and add those years to their own, extending their life and youth while draining the human of the same years and youth, resulting in formerly young humans to grow eldery, ill, or even die instantly. Alternatively, these two witches were also able to give years to humans, restoring their youth and health just as quickly.
Vampire Diaries witches don't have longevity, but there is instances of certain witches creating spells to make themselves age slower.
In conclusion, Supernatural witches are ultimately humans, while Vampire Diaries witches are supernatural beings.
Theories
The following theories have not been proven, but are possible in the Supernatural Diaries roleplay.
Vampire Diaries witches being considered a supernatural race go to purgatory when they die (The equivalent to The Vampire Diaries "The Other Side").
Crowley, being the son of a Supernatural witch, was likely one during his human life and his power as a demon could be related to the fact that may be able to draw power from other demons even in death.
Vampire Diaries witches could have been created by Eve, opening the possibility that there is an Alpha Witch that is the ancestor to all Vampire Diaries witches.
The Vampire Diaries has stated that vampires can not be witches as well because Vampires are abominations of nature, rendering them unable to draw on nature as a source of power. However, given the fact that Silas was an immortal and therefore also an abomination to nature who could still use magic, it's possible Vampire Diaries vampires could learn to use magic. Tying Supernatural together with this theory can explain the how and why--similar to how any human can learn witchcraft. Demons and Angels are also seen able to use witchcraft.
