The first known hybrid, and the only current hybrid is Brielle Salvatore, the daughter of the vampire Stefan Salvatore and the witch, Dia Kenner, created through a ritual involving the blood of both parties, and carried for nine months inside of her mother, before being born.
Witch-Vampire hybrids were not known to have been able to even be possible, but somehow the pregnancy of Dia broke all sort of standards to make it possible, and also making Brielle the first biological child of a vampire, after their transition, until Niklaus Mikaelson's daughter Hope was born in 2010.
Considered an abomination to nature, and an unfair balance of power by many witches, the witch-vampire hybrid can be considered to be endangered, since many witches see it as wrong, and want to stamp out the species, targeting Brielle and her parents to try and stop the possible budding species before they can develop. Every species has its weakness, and much like their cousin, the werewolf-vampire hybrid, they are considered too powerful to be allowed to live.
The witch-vampire hybrid is distantly related to the other two supernatural hybrid species; the werewolf-vampire hybrids and the witch-vampire-werewolf hybrid. (Of which Hope Mikaelson is the first and only known in this species.) This hybrid is different than that of the Heretics, in the fact that they are a true hybrid, rather than a coexistence of both.
After the birth of the first hybrid, Brielle, nature deemed the child to be an imbalance of power, and any other witch attempting to perform the ritual to give them a child to a vampire will be unsuccessful; as nature will not allow another.
Super Strength: The strength of a witch & vampire hybrid is not as good as a vampire, but, it's pretty close. Even not having a large amount of physical strength isn't necessarily a drawback, considering they also have magic.
Speed: A witch-vampire hybrid can use the same amount of super speed that a regular vampire can use.
Healing: They can heal both simple and more grievous injuries, and only slightly slower than that of a normal vampire. The healing process of a witch/vampire is only about a second or two behind the average "pureblooded" vampire. Additionally, wood doesn't cause slow them down like a vampire.
Compulsion: The compulsion skills of a witch/vampire are especially strong, given their tie to nature and magic. Their compulsion tends to last longer than normal vampires, but, they cannot compel other vampires or other hybrids. (Both werewolf crossed with vampire and witch.) The same rules of compulsion still apply-as in they can't compel supernatural creatures, such as regular werewolves and witches as well.
Magic: This hybrid combination, while a witch previously could not be a witch & a vampire at the same time, now makes it possible to be both witch and vampire. This includes spell casting, and potion making in addition. They're just as powerful, if not more than a regular witch.
Overexertion: Normal witches can become over exerted if they use too powerful of a spell, or if they use magic for too long, the hybrids don't have this problem. Since the original hybrid, Brielle O'Bryan-Salvatore, was created with a spell, the limits of a witch-vampire hybrid's powers are not limited by nature-as they can use their existence as a constant siphon of power. They can constantly use their own life force to draw their power from.
Transformation: Any witch-vampire hybrid has the ability to turn a witch into a witch-vampire hybrid. A human cannot be turned into a witch-vampire hybrid, and any human administered the blood of the hybrid will not be able to complete the transition, and not be able to turn into a vampire or a hybrid.
Immortality: A witch-vampire hybrid can be born, but with only one born hybrid currently known in existence, (Brielle Salvatore) the aging process stops at the transition into a hybrid. If, for some reason, another hybrid were to be born, either the children of the first hybrid, or another ritual was somehow performed, they can choose to stop the aging process at any time. Once the aging process is stopped, it cannot be resumed again.
Channeling: Like any other witch, the hybrids can channel the magic of an object or another witch to help aid them in the potency of the spells, or in making a certain spell longer, or to give them just a little bit of extra magic to help them to do some truly extraordinary magic.
Divination: Witch-Vampire Hybrids can have the ability to have powerful premonitions and be able to see into the future like a regular witch, but this ability sort of comes and goes just like as with a normal witch. Their vampire side does not hinder this in any way.
Empathy: Since their emotions are heightened, due to their vampire side, the witch's ability to sense other's emotions and reading others is particularly empowered as well.
Vervain: When vervain comes into contact with them, either through a charm or a necklace, or if it's put into food or drink can weaken their vampiric powers, but will not cause blisters to the skin when makes contact, as it does with their vampire "cousins". Any vervain in the air can weaken them, and will slow down their healing process, however. They can consume it, and build a tolerance to it, even if it will taste disgusting and almost painful to consume, but in any event cannot be immune to it completely. (Just like a regular vampire.)
Sunlight: A witch-vampire hybrid will not burn up in the sunlight, due to the witch part of their DNA, but the sunlight will weaken their magic, and after being exposed to it for long period of time, they can be given bad sunburns, that appear quicker than a normal human or a vampire, and can often result in painful blistering. A daylight ring can be crafted to protect them from the sun.
Bloodlust: The hybrid of witch & vampire will suffer the same kind of blood lust that a vampire would. They can also learn to control it, and when their bloodlust is activated, the veins around their eyes will protrude, and their eyes will darken & turn red like a normal vampire.
Staking: While wood doesn't slow them down or cause them any sort of weakness, being staked in the heart with a wooden stake will kill them, and they will mummify like their vampire counterparts.
Fire: A witch-vampire hybrid can be set on fire, and if not put out before it consumes them, they will die. If they fire is put out immediately however, they still have a chance to live and survive the attack.
Beheading: If the head is severed from the body of a witch-vampire hybrid, they will die. There is no way they can be protected from that.
Ripped Heart: If the heart is torn from the chest, since this would kill a witch or a vampire, would therefore kill a hybrid as well.
Lobelia flower: This is a flower that can weaken the powers of a witch-vampire hybrid, and affects concentration, and will weaken the powers of a witch-vampire hybrid just as it would to a regular witch. It will not blister them as vervain will, but the weakening effect is about the same. (But, with magic. Their vampiristic abilities will not be affected.)
Magic: As with any other sort of supernatural or non supernatural creature, they can be affected by both Dark magic and magic aimed to try and weaken them.
Distraction: The ability to be able to be distracted from focusing all their power on a spell or ritual can still effect both the potency and the effectiveness of a spell, and in some cases, can cause it not to be performed successfully. The spell working all depends on the focus and determination of the hybrid performing it.
Trauma/Fear: Any amounts of massive fear of strain put on a hybrid can also weaken their abilities, and if strong enough, make their powers useless altogether. This can be overcome by overcoming the fear, or solving the problem. (The strongest a witch can be is unafraid and when she feels safe.)
Bloodline: If Niklaus Mikaelson, the originator of the bloodline in which all witch-vampire hybrids spawn, dies permanently, the entire witch-vampire hybrid race will die along with him. This is due to the fact that Stefan Salvatore is part of Klaus' bloodline-and all witch-vampire hybrids are created through his daughter, Brielle Salvatore; his blood gives her vampiric abilities. Therefore all the witch-vampire hybrids are indirectly part of Klaus' bloodline.