The Vampire Diaries universe continues to expand years after the end of the main series, with two successful spinoffs that fans just can't get enough of - the recent Legacies and the show's first spinoff The Originals. Each series is filled with all sorts of supernatural beings, from vampires and werewolves to witches and hybrids. All these mythological creatures were presented in new and unique ways, veering away from more traditional representations, which is what made these series so interesting to watch.
Considering that The Vampire Diaries and The Originals are set in the same universe, viewers would expect them to follow the same set of rules when it comes to the world of the supernatural. And for the most part, they do, but there were several times when previously established facts were contradicted in The Originals with no real explanation.
When Klaus broke his hybrid curse in The Vampire Diaries, he couldn't turn others into hybrids without using the doppelganger's blood. It was clearly shown that for a werewolf to become a hybrid, they have to die with Klaus' blood in their system and then feed on Elena's blood when they come back to life in order to complete their transition.
However, in The Originals, when Hope turned Henry into a hybrid he died with her blood in his system and then fed on her blood again, and Elena's blood was never needed. This completely contradicts everything that happened in The Vampire Diaries as it implies that Klaus should've been able to make hybrids by giving them his own blood both times.
One of the many supernatural creatures that dominated the two series were the witches. In The Vampire Diaries, it was established that there are certain types of magic that witches cannot practice without withstanding some horrible consequences. In the few instances that Bonnie had to use dark magic, the spirits turned against her, either by hurting her grandmother who was on the other side or by taking away her ability to use magic altogether. Eventually in "The Walking Dead" the use of dark magic actually led to Bonnie's death.
However, in The Originals, the witches of New Orleans are constantly doing spells that definitely qualify as black magic, by sacrificing animals and using dark objects, and yet nothing bad ever happens to them.
In The Vampire Diaries, it was mentioned several times that werewolves were a rare species that was very difficult to track down. As their venom is lethal to vampires, it was said that they were hunted down and killed, leaving only a few remaining packs. Moreover, when Klaus was looking for werewolves so he could build his hybrid army at the beginning of season 3, he and Stefan spent several months looking for them, and only found one pack.
Meanwhile, the spinoff is jam-packed with werewolves! The Crescent pack was constantly growing in numbers and each season was introducing more and more werewolf characters. As their rarety had already been established, this inconsistency was one of the many things that didn't make sense about the TVD universe's werewolves.
When the concept of werewolves was introduced in The Vampire Diaries, it was presented as a curse. It was heavily emphasized that turning into a wolf every month was an excruciating process as they had to break every single bone in their bodies and especially their first transformation could last for hours. When Tyler was preparing for his first full moon, he found a video of his uncle Mason's first transformation and was horrified by how long the footage was. And later when he began turning, fans got to see firsthand how agonizing werewolf transformations could be.
However, when Hope turned for the first time in The Originals, all she needed was a quick pep talk from Klaus, and then she transformed within a minute, barely feeling any pain.
When the Salvatores were searching for a way to kill the Mikaelsons in The Vampire Diaries, they discovered the last remaining piece of white oak, a part of the Wickery Bridge that Rebekah didn't burn. They turned that into stakes which they intended to use against the originals but things didn't quite go as planned and the audience was led to believe that Klaus destroyed all of them. By the time the Mikaelsons left Mystic Falls the White Oak stake that was fortified by Esther, was the last remaining piece and one of the most powerful objects in The Vampire Diaries.
But in The Originals, white oak kept appearing out of nowhere. And in the last season, Klaus brought back one of the stakes that he supposedly destroyed all that time ago.
Even though the originals were immortals, there were still ways for them to die. The Vampire Diaries saw the deaths of three original vampires as Mikael, Finn, and Kol were all murdered with white oak weapons, and each one of them burst into flames following their stabbing. This pattern continued in The Originals as Mikael burst into flames again the second time he died by White Oak. And another time when Mikael stabbed Klaus with the same stake which had been neutralized with magic, Mikael was exasperatedly waiting for his body to burn, to ensure that he had died.
However in "When The Saints Go Marching In" Klaus and Elijah stabbed each other with the last remaining white oak stake, but instead of burning they just turned into ashes.
The Vampire Diaries changes conventional vampire lore, and while TVD's vampires do burn in sunlight, they can obtain magically enhanced rings to protect themselves. However, in the course of The Vampire Diaries, there were several occasions where characters stood in the sunlight without their rings and they didn't die. Instead, their skin would slowly begin sizzling, giving other characters plenty of time to come to their rescue.
But in The Originals, this is not the case, and instead, as soon as a vampire sees the sunlight without a daylight ring, they burn to their deaths.
It's quite rare for TVD characters to have a permanent death as there's always a chance for them to come back in one way or another. In season 5, Bonnie became the bridge to the other side, which meant that every supernatural being who died would have to pass through her in order to pass to their afterlife. And when the other side was collapsing, Bonnie was able to bring people back to life by reversing the function of the spell that made her the bridge. The only way to get out of the other side was through Bonnie.
But in The Originals, there were several other characters that were resurrected with magic alone, and there was never any explanation of how that happened.
In The Vampire Diaries universe, vampires are known to be a very powerful species but their many strengths come with various weaknesses, and among them is werewolf venom. Even though vampires are far superior to werewolves when it comes to strength, a single bite from them is inevitably fatal. There were several occasions in The Vampire Diaries when a character suffered a werewolf-inflicted bite and each time they would get seriously ill, violent, and begin hallucinating but wouldn't die until at least a few days later.
However, the effects of a werewolf bite in the original show differ from the spinoff. In The Originals, the vampires would get sick much faster and succumb to their injuries mere hours later.
As the oldest and the first vampires in existence, the Mikaelson family is known to be extremely powerful. They were first introduced in The Vampire Diaries which quickly established their reputation as the strongest creatures in the world who were really hard to kill.
But in The Originals, this doesn't seem to be the case anymore. Their power comes and goes, and at times they get overpowered by younger, supposedly weaker vampires. It seemed like their strength would increase or diminish to suit the plot and that was very inconsistent.
