Serana

Serana is an ancient pure-blood vampire in The Elder Scrolls V: Dawnguard. She is enterprising and friendly, but also lonely due to her troubled childhood and her mother's self-exile, which is why she confides in the Dragonborn.

Origins
Her exact age cannot be determined, but she is believed to predate the Alessian Empire from the early First Era.

She is one of the few pure-blood Vampires known to exist. Pure-blood vampires are individuals who are granted vampirism directly from Molag Bal, the creator and patron deity of Vampires. The process is somewhat similar to the creation of the first vampire, Lamae Beolfag. Serana gained her vampirism through a ritual in which members of her family pledged themselves to Molag Bal. Females like Serana and her mother, Valerica, who survive the horiffic ordeal are dubbed "Daughters of Coldharbor".

Prophecy
Her father, Lord Harkon is leader of a Volkihar vampire clan based in Castle Volkihar. He discovered an ancient prophecy called the Tyranny of the Sun which if enacted would allow Vampires to roam the world freely without the fear of weakness from the sun; but to do so, he required two Elder Scrolls, Auriel's Bow and Serana for a ritual sacrifice.

In response to this, her mother hid her away with one of the Elder Scrolls in a sealed sarcophagus within Dimhollow Crypt for thousands of years to protect her from her father. She fled to the Soul Cairn with the other.

Awakening
The Dragonborn is sent to Dimhollow Crypt to investigate what vampires are looking for there. Serana is discovered in the crypt and is set free. She asks the Dragonborn to help her get home to Castle Volkihar. If the Dragonborn is a vampire when freeing her from the sarcophagus, it will yield different speech options than if the Dragonborn isn't a vampire.

Chasing Echoes
Serana indicates her desire to locate her estranged mother, Valerica. She believes that Valerica may have left a clue to her whereabouts somewhere in the courtyard of Castle Volkihar. The Dragonborn must travel with her and infiltrate the castle to find Valerica whereabouts.

Beyond Death
It is discovered Valerica fled to the Soul Cairn vie a portal in Castle Volkihar. The Dragonborn and Serana must travel there and retrieve the Elder Scroll Valerica took with her.

Unseen Visions
The Dragonborn and Serana must travel to Ancestor Glade to learn how to read the Elder Scroll that will show them where to obtain Auriel's Bow.

Touching the Sky
Serana travels with the Dragonborn to the Forgotten Vale to seek Auriel's Bow.

Kindred Judgement
Serana travels with the Dragonborn back to the Castle Volkihar to confront Lord Harkon.

Follower interactions
Unlike regular followers, Serana displays advanced behavior and situational awareness: In addition, once the Dawnguard questline is completed, she can continue to serve as a follower, but does not have the same set of Follower commands that other followers have. She will equip enchanted rings, chains and circlets, as well as both light and heavy armor. When outdoors, however, she wears her hood which displaces any circlets. Since she cannot be killed, it makes her a very reliable ally.
 * If Serana is outside during sunlight hours, she will always don a hood.
 * She will comment on the weather; however, be it rain or shine, it's typically a complaint.
 * She will interact with her surroundings. If the Dragonborn is standing still, she may walk around, sit down and even interact with workstations like a grindstones, forge or alchemy lab.
 * If nearby an ore vein, she may begin mining, despite not having a pickaxe in her inventory.

She can also be asked to bite the Dragonborn, which grants the ability to become a Vampire Lord, however this cannot be done if she has been asked to cure herself of vampirism. While she is a follower, the Vampire Lord's Drain Life spell is weakened.

Combat
In battle, Serana proves herself to be a powerful necromancer. She will frequently raise the corpse of both humanoids and creatures, even very powerful ones, including Dremora Catifs, (which do not disintigrate into ash when the spell ends).

She prefers to dual wield Vampiric Drain and Ice Spike spells, but may use Lightning Bolt for attacking at range. She will switch to melee combat when her magicka runs dry with her default weapon being an Elven Dagger. She will equip stronger daggers and swords if given to her and will even wield two-handed weapons.

She will also use a staff if given a powerful enough one. The staff may change in appearance to Falmer style, (metallic grey with a forked end), when she uses it. This change in appearance persists if the staff is taken from her.

Although her exact stats are not known, due to the fact that she has a high Sneak skill (she has the "Silent Roll" perk), she prefers Light Armor, and she starts with a dagger, it can be assumed that she is meant to be an assassin-type follower.

Trivia

 * Serana is voiced by Laura Bailey.
 * Serana will politely refuse a proposal of marriage, complaining about her unease with temples and complicated history.
 * Once the Dawnguard questline is complete, she can be asked about curing her Vampirism. Should she agree, she will leave to see Falion for a cure. She will return to Fort Dawnguard after a few days, cured, yet she will still use the same dialog as though she were still a vampire and will still wear her hood when outdoors. If the Dragonborn persistently asks her about her potential pursuit of a cure at inopportune times, Serana may become upset and the Dragonborn will lose that dialog option.

Bugs

 * She might get stuck in one place as if being ordered to wait. Throwing her off her feet with a level three Unrelenting Force can fix this.
 * Sometimes when sneak is entered and then left, she'll continue to be sneaking. Entering a city should fix this.
 * If told to "Wait Here", the option to "Follow me" may not appear when spoken to. If the cell is unloaded, she may disappear forever and it may only be fixed with console commands.
 * If the main questline for Dawnguard is finished, asking to part ways may fix this. If she will not continue following during the questline, she will appear at scenarios requiring her. If not, using ally commands to move her into the area may also work.
 * It may be impossible to recruit her again once dissmised. The only know fix is to reload a save back when she was a follower.
 * If she "dies" she may not get up until entering a new area. She will slide along the ground as if "dead" and can even still be talked to.
 * After using her spells to defeat an enemy, the crackling sound from her spells may continue to be heard around her despite the spells no longer being active. The sound usually fades overtime though.
 * Fix: Enter a new area and the sound should go away. Doesn't always work, and doesn't work on some NPC's who also have this glitch (i.e. Anska).
 * After the Vampires Questline is complete, when dismissed she may say things such as, "I'll meet you at Darkfall Cave" or "I'll be at the glade" even though you've already been there and are done with the quests required for them. Dismissing her many times until she says something different should fix this.
 * When wearing armor given to her instead of her standard attire, she sometimes doesn't wear her hood when outside and sometimes wears it when indoors.
 * Even though she can be seen rolling forward while sneaking she still sets of pressure plates and tripwire, however for the Silent Roll perk Light Foot is a required perk.
 * Serana won't don armor (chest and legs slot), even if it is beter than the Vampire Royal Armor she wears. Tested with armor types from elven, steel, steel plate, orcish, and ebony (unenchanted and enchanted). She will however wear special armors such as Nightingale and Thieves Guild armor.
 * When she is brought to a place with a specific animation, such as Molag Bal's altar or Cicero's room in the Dawnstar Sanctuary, she will perform the action done there (crouching with her hands on her head and curling into fetal position, respectively). This likely happens due to the fact that she is meant to interact with her environment, unlike other followers.
 * When first encountered during Bloodline, she becomes a possible candidate for the multiple followers exploit.