A succubus (plural succubi) is a female demon appearing in dreams who takes the form of a human woman in order to seduce men, usually through sexual intercourse. The male counterpart is the incubus. Religious traditions hold that repeated intercourse with a succubus may result in the deterioration of health or even death. A succubus may or may not appear in dreams and is often depicted as a highly attractive seductress or enchantress; whereas, in the past, succubi were generally depicted as frightening and demonic.
If that would have happened, she would probably still be in Mystic Falls. The actress who portrays her, Melinda Clarke, is currently busy by starring in the TV series Nikita (one of the main roles) on The CW. The writers probably wanted to bring storyline for malach creatures or the true nature of The Darkness. After Nikita ended Kelly returned breifly.
In the initial few episodes of the first season, Bonnie Bennett states she is psychic, and makes accurate predictions about the future with visions.
Later on, this story line was scrapped, and she was stated to be a witch. She has not used her psychic abilities since.
Weather Manipulation: Initially, in thePilot, Damon Salvatore had the power to create fog from nothing, however, this power was thought to be too supernatural, so it has not been used by any vampires since. This power was later used by Bonnie Bennett, a witch, after harnessing the power of her deceased ancestors.
Compelling Animals: Damon Salvatore also used a crow to spy on Elena Gilbert, and also Stefan. A different crow was seen in a flashback in 1912. After Damon killed his crow, he hasn't compelled any other animals, while neither has any other vampires.
Lie Detection: InDaddy Issues, Jules tells Caroline Forbes that werewolves have the ability to tell if someone is lying. Although Klaus is part-werewolf and should have all werewolf abilities, he had to rely on Rebekah Mikaelson to find out that Stefan was lying to him about Elena being dead, and could not tell when Elena lied about Mikael being dead. It is possible that Jules was lying to Caroline to intimidate her, or that just a few werewolves can detect lies.
Klaus was originally stated to be the oldest vampire in the history of time, and the most dangerous and feared original. Later, more originals were introduced and it was revealed that he has 2 older siblings who were also Original Vampires (Elijah and Finn), as well as a third older sibling who died before Niklaus was even born (but who was never a Vampires). It is also revealed that his mother and father are still alive, making his father, Mikael, the oldest member of the Original Family.
It is also stated that Niklaus was not really a vampire at all and really a vampire/werewolf hybrid. This idea was obviously added later onto the storyline last minute, as at first, all characters in the TVD universe believe the Sun and Moon Curse is real and believe Niklaus to be a vampire, including Katherine, who claimed to know all about Niklaus. Then suddenly all characters in the TVD universe are aware that Klaus is a hybrid with no explanation of how they became aware, and there is no mention again of the Sun and Moon Curse.