Ascendant

Ascendants are mystical relics which were previously owned by the Peterson Family. An Ascendant can be used to harness the power of a celestial event to create a portal to a different dimension and allow a person to travel through it. The Gemini Coven in particular used the relics to create Prison Worlds in order to trap former and current members who had broken their laws away from innocent humans. An Ascendant was first seen in Black Hole Sun when Clare Blackwell used a locator spell to find the Ascendant to the 1994 Prison World, only to find that Malachai Peterson had it all along.

There are Three  known Ascendants to have existed alongside of their respective Prison Worlds: one that could access the 1903, 1994, and the 1933 Prison Worlds. Each replica within the four aforementioned prison worlds is meant to be used to return to the living world. Initially there were no longer any Ascendants in existence, as the previous 1903 and 1994 ascendants were destroyed with magic and their copies destroyed in the prison world upon the death of the Gemini Coven's leader, Kai, in I'm Thinking Of You All The While. However during the events in It's Been a Hell of a Ride, Bonnie aided Josie and Lizzie in creation of another one, which they used to imprison Kai once again.

History
For now, not much is known about the Ascendant other than its main usage - to harness the power of a celestial event and open a portal to another dimension, usually, a dimension specifically created to imprison someone. It can also determine the center of where the celestial power should be harnessed in order to create the portal. It is also known that it belonged to Malachai "Kai" Parker's back in the state of Oregon in the Pacific Northwest.

Throughout The Vampire Diaries Series
In Black Hole Sun, the Ascendant was first mentioned by Kai after Damon gets upset. He claimed that in order to escape this dimension, Bonnie needed to channel the power of the solar eclipse through the Ascendant which will open a portal to the living world. He then reveals that the last time he had it was in Oregon, therefore, Bonnie uses his blood to perform a locator spell. After failing for some time and a few encouraging words from Kai, Bonnie finally manages to do the spell and figures out that Kai had it in his pocket the entire time. He then says he just wanted to make sure her magic is working as it should be. Later on, he is using the Ascendant to determine where the eclipse's power should be harnessed when Bonnie and Damon discover he's a mass murderer who slaughtered his entire family and is, in fact, a witch. Bonnie immediately refuses to release him and later on, she and Damon make plans to steal the Ascendant, escape and leave Kai alone in this place, though he overhears them and claims that he'll kill Bonnie by draining her magic if they don't work together.
 * -|Season Six=

In The World Has Turned and Left Me Here, Bonnie discovers that the Ascendant and the spell to activate it are a Bennett invention which the Gemini Coven used to make sure that Kai would never get out of the time loop. Therefore, only Bonnie can use the spell and the Ascendant. She kills Kai and prepares to get her and Damon out of the time loop. However, Kai returns as the witches made sure that he never got out of the time loop, not even by dying. He injures Bonnie with a crossbow bolt and then fights Damon who is also injured. Bonnie uses her magic to incapacitate Kai before throwing Damon the activating Ascendant and allowing him to escape alone, leaving her trapped along with Kai in the time loop. The Ascendant is destroyed by the ritual.

In Because, Bonnie stole the 1903 Ascendant from Lily and then destroyed it in order to prevent Kai and the Heretics from getting out of the prison world.

In It's Been a Hell of a Ride, Bonnie helped Josie and Lizzie in creation of another ascendant, as it was the only way to stop Kai. Bonnie had said to Kai that there is no eclipse, which he could use to escape this time, but it is unclear if another celestial event was used, given the creation of the previous two.
 * -|Season Eight=

`Throughout Legacies Series
In There's Always a Loophole, when magic is nullified at the Salvatore Boarding School for the Young & Gifted, Josie finds a box in Alaric's office that was previously cloaked. She later breaks into the box and finds the Ascendant that was used by Bonnie in 2018 to imprison Kai Parker. The Ascendant looks familiar to her and Lizzie and Josie recognize it from the Merge research.
 * -|Season One=

In I'll Never Give Up Hope, Josie continues to try and pry information from Alaric about the Ascendant and how it relates to the Merge. Alaric tells her that it is nothing to do with the Merge and that she should drop it. After confronting her father, culminating in a public argument, he comes clean and tells her that it's a "lock" to a prison world and it holds their murderous uncle - Kai Parker. He is the only other living member of her and Lizzie's lunatic family. Lizzie wants to go to the prison world - he's been through the Merge and believes that he's got to have answers. They can't, however, Josie returned the Ascendant to Alaric and that contacting him is their last resort, seeing as he killed his own family and his sister on her wedding day.
 * -|Season Two=

In This is Why We Don't Entrust Plans to Muppet Babies,

In What Cupid Problem?, Lizzie, Josie and the witches of the Salvatore Boarding School for the Young & Gifted create a new ascendant and, therefore, the 2028 Prison World, in order to transport the mora miserium to the dimension to lock it away. Unbeknownst to them, Alyssa Chang linked the spell to the 2018 ascendant, thereby sending Alaric, Lizzie and Josie there instead of the newly created 2028 Prison World.

In You Can't Save Them All, in order to complete their escape, Josie created doors within the world by siphoning the world's magic. Josie's spell allowed them, as well as Jade and Wendy, to escape; however, the world became unstable and eventually collapsed within itself. As a result, the Ascendant on the mortal plane broke with the destruction of the world.

Usage
Ascendants allow a witch to harness the power of a celestial event (a solar eclipse, the Aurora Borealis, etc.) to open portals thereby giving one the ability to transcend dimensions. With the blood of a Bennett witch, an Ascendant will be activated by the light of the celestial event. Anyone standing within the circle of light, while holding the Ascendant can then jump through the portal.

Additionally, an Ascendant can be used to pinpoint the positions of celestial bodies. Thus, allowing one to determine where the power of the celestial event is concentrated.

Trivia

 * Since powerful spells require a binding object to keep them active, it is possible that the Ascendants were used for this purpose by the Gemini Coven when they created the Prison Worlds. This is further supported by the fact that the Ascendants can open a portal between dimensions.
 * In The World Has Turned and Left Me Here, the 1994 was destroyed when Damon escaped the Prison World.
 * However, in Do You Remember the First Time?, Bonnie managed to fix the 1994 Ascendant again.
 * In Fade Into You, it's revealed that Jo has the present day 1994 Ascendant in her possession to ensure that no one could rescue her brother Kai from his prison world.
 * Though it was initially believed that a Bennett witch needed to perform the spell on the Ascendant to create a portal, Kai eventually figured out that he only needed magic and Bennett blood to use it. This led him to steal Bonnie's blood and the magic from Jo's blade to flee the prison world without Bonnie.
 * In I Alone, Kai destroyed the actual 1994 Ascendant; first by breaking it apart, then by throwing it against a tree, and finally by using his stolen magic from Liv to set the Ascendant on fire, though Elena futilely attempted to save it with no success.
 * There are two Ascendants for each known prison world—one in the living world and another in the prison world itself.
 * The Ascendant can only be activated by Bennett blood.
 * This points to the theory that a Bennett witch created the spell and enchanted the object.
 * This wouldn't be the first time a Bennett witch has utilized witchcraft by enchanting objects, as Emily Bennett did the same when she weaponized the Grayson Device.
 * In A Bird in a Gilded Cage, it's revealed that the leader of the Gemini Coven doesn't need a celestial event to activate the power of the Ascendant, he only needed the blood of a Bennett witch.
 * Damon explains in A Bird in a Gilded Cage, that Ascendants can't travel between the real world and prison worlds, which is why there is a copy in each prison world.
 * In I Never Could Love Like That, Damian gives his mother Lily the 1903 Ascendant.
 * In Because, Bonnie stole it from her and destroys it.
 * In It's Been a Hell of a Ride, Bonnie helped Josie and Lizzie make another one, which they used to imprison Kai once again, in a new Prison World.