Mercedes (original name unknown) is an angel who was turned into a vampire.
Since the immortals Amara and Silas, nature has been creating doppelgangers. But the doppelgangers and their look-alike ghosts create disturbance in heaven. So when a new doppelganger is born, angels in charge send minions to earth to kill doppelgangers and destroy their spirits. Mercedes was sent from heaven to kill Tatia, which she did after Esther used her to block Klaus' werewolf side. But before she could destroy Tatia's spirit too, Elijah and Klaus fought to stop her, ended up turning her into a vampire for revenge. As a result, heaven sent another angel to destroy Tatia's soul and complete Mercedes' mission, but they didn't accept Mercedes back for being a vampire now, therefore impure.
Now trapped on earth, Mercedes is very unhappy and doesn't enjoy life. Her angel essence, despite being suppressed due to being a vampire, still manages to give her a slight ability to stay under sunlight, but only for a short time, like an hour or two. And she is considerably stronger than a vampire at her age is supposed to be. She longs for her angel times, back when she had access to heaven. Other angels abandoned her too because of what she is. She wants to kill herself and end her suffering, but fears of getting trapped on the other side forever. In time her fear took the best of her, and now she is basically a freak who remains in the shadows, afraid to go out there and live a normal life, while trying to hold on to her humanity in her own wicked way.
Once she discovered that she could compel other beings including Angels she began to enjoy her new powers, once God discovered that Mercedes could compel Angels he realised that she was a threat to heaven as she could potentially compel her way into Heaven and usurp him from power. Fearing this new abomination, he sent his highest Angelic warriors the Gibborim to hunt her down and destroy her, she uses her new power to compel the Gibborim and hide from them.
Angels are considered pure souls. That is why a vampire, an impure creature and an abomination, is not accepted to heaven.
In some cases angels do not want to get their hands dirty by killing a person, so they choose to go for hard ways. It is rumored among the angels that Elena was one of these cases. It is said that the angel that was assigned to kill Elena caused the accident and made Stefan's way to Elena. This way the angel hoped Stefan and Elena would fall in love, and eventually she would be turned into a vampire and therefore become impure and get banned from heaven for good.
The source of an angel's power and strength is their access to heaven. Once this connection is severed somehow (falling, becoming impure, a crisis in heaven, etc) the angel is rendered powerless.
It is stated that angels do not discover most of their powers & abilities until they need them, which indicates that there are many. Known angel powers and abilities are:
- Immortality: As celestial beings, angels will live forever unless they are killed.
- Adaptation: Angels can adapt to their opponents, which gives them the strength and skills they need against them.
- Phase changing: Angels can be corporeal or incorporeal at will.
- Wings: Despite mainly used for flight, wings can also be used as a defensive shield or intimidation in some cases. They appear and disappear by the angel's will.
- Empathy: Angels can feel the emotions and thoughts of people, which gives them an advanced ability to predict what people's intentions are.
- Compulsion: As a Angel-Vampire Hybrid, she can compel, Humans, Vampires (except Originals), Angels and unlike standard and Original Vampires she can compel Witches.
Known angel weaknesses are:
- Vampires: Due to their dark natures, angels have difficulty in predicting vampires.
- Disconnection to heaven: If an angel falls or becomes impure, or anyhow their connection to heaven is severed, their access is not granted anymore. This leaves the angel powerless and simply human for the rest of their lives.
- Diamond: Despite angels can get through solid matter in their incorporeal status, they can't get through diamonds. Diamonds are also the only known thing that can hurt angels even when they are incorporeal.
- Basic human weaknesses: Despite being celestial creatures, in earth's atmosphere their body functions as humans. This gives them basic human weaknesses, and they can easily be killed.