Effects of the Curse
True love's kiss will not break a Dark One's curse if the Dark One doesn't want to give up the power. Nor will true love's kiss work if both people involved are Dark Ones. Everyone who becomes a Dark One always claims that they will never give in to the darkness, but fail; Emma proved the strongest at resisting, but gave in when she refused to let Hook die by turning him into a second Dark One. Hook later pointed out that Emma only gave in out of love; likely being born of her parents' True Love gave Emma a stronger will than others possessed by the darkness. Dark Ones don't need sleep, as the power of the Darkness keeps them energized. However, it appears this is optional in A Land Without Magic, as Mr. Gold was seen sleeping after magic was brought to Storybrooke; Hook also never mentioned having trouble sleeping when his memory of being a Dark One was erased. Dark Ones such as Rumplestiltskin and Emma Swan developed hobbies to pass the time instead; Rumplestiltskin spun straw into gold and Emma made dreamcatchers. All Dark Ones find it irresistible to make deals.
According to Cora and Mr. Gold, when the Dark One is killed without the dagger, she/he will expel the power of the darkness, with no new Dark One, and the curse will "pass from this world". Despite this, the previous host can be resurrected through the Vault of the Dark One, but at the cost of another's life.
Dark Ones are drawn to their dagger, as it "whispers" to them to take possession of it. Emma later finds out, that she can still hear the whispers of the Dark One dagger; Mr. Gold hadn't counted on this, as all past Dark Ones are dead, and Emma was an exception.
As the Darkness takes ahold of an person and makes them a Dark One, each individual is affected differently. After Nimue becomes the first Dark One, by using her newly found magic for evil, her skin transforms green, and hey eyes change their shhape. For Zoso and Rumplestiltskin, their skin transformed into a gold hue. Emma's appearance changed, though not as drastically as her hair became pale and her lips appeared to turn red. Hook as a Dark One, changed the least. He simply had messier hair and a somewhat quirky demeanor - it should be noted that Emma and Hook, were the only Dark One's not to be turned through the act of murder.
- Darkness Generation and Control: As a Dark One, the individual can freely create, control and manipulate pure darkness and shadows to their will. They are the pure human embodiment of all evil, chaos and darkness in the world.
- Immortality: The host stops aging when gained their powers and have proven immune to disease and most forms of human death. (However, may be minor damage such as being cut by a sword, and will have to use his powers to heal).
- Teleportation: The ability to move from one place to another at will.
- Telekinesis: Being able to manipulating objects or people without physically touching them.
- Pyrokinesis: The ability to create and manipulate fire.
- Accelerated Healing: When the host uses their healing abilities, their hand will glow with purple and after having approached the wound, it will heal completely, leaving no visible sign, however, they are unable to treat some types of poisons such as ddreamshade.
- Transfiguration/Shapeshifter: The ability to change the the physical aspect of a person or object.
- Superhuman Strength and Speed: Enhances traits that allow the host to be incredibly fast and strong in melee combat.
- Arcane Knowledge: Various hosts have demonstrated an almost infinite knowledge and understanding of spells, potions, and other topics related to magic, allowing him to do impossible things for common wizards.
- Summons: The ability to summon objects or beings through the magic.
- Heart Extraction: Being able remove the hearts of other living beings without killing them and use them to control the owner or kill them by crushing the heart. This was the act that created the Dark One.
- Perception: Being able to sense when someone calls the host's name (when called three timed) or when someone's close to them.
- Resurrection: If the host dies without having passed the title of Dark One to another being, they can be resurrected via Dark One Vault, if another person decides to open it, giving up his life as a result.
- Technopaty: Magic also allows the host to manipulate technology.
The Darkness is a sentient force of pure evil. It appears as a black mass of tendrils without a host. It's later revealed to be the embodiment of Nimue's magic/soul, which became corrupted after Nimue used the magic granted to her by the Holy Grail to kill Vortigan (the Darkness is immortal, this is a result of Nimue drinking the waters of the Holy Grail). She, along with the other consciousnesses of the Dark Ones, continue to reside in their successors. When one becomes a Dark One, a mental image of their predecessor appears to guide them in how to use the Darkness's powers. The waterfall in the pocket dimension inside the Vault of the Dark One is liquid darkness.
To keep Nimue from causing damage, Merlin created the Dark One's Dagger via a tethering spell to control her. However, she stole it and later used it to turn Merlin into a tree. Nimue would later be stabbed by the dagger, allowing her magic and consciousness to possess her attacker. Thus anyone who killed a Dark One gained magic and the Darkness grew more powerful with each new Dark One. This began the Dark One line. Between Nimue and Gorgon the Invincible, there were at least 18 Dark Ones. After these 20 came Zoso and Rumplestiltskin.
When Mr. Gold's heart is in danger of being devoured by the Darkness, the Apprentice attempts to seal it in the Sorcerer's Hat; it escapes and fatally wounds him in an attempt to make him its new host. It tries using Regina next, but Emma uses the dagger to force the Darkness to possess her instead.
Though it's believed Emma has fallen under the Darkness's sway, flashbacks reveal that she remains un-corrupted by it; in truth she was planning to transfer the Darkness into Zelena after she gives birth, and then slay her to put an end to the Darkness. The reason for this is that half of the Darkness was transferred into Hook to save his life; he had received a wound to his neck from Excalibur, which was unable to be healed, thus forcing Emma to do this out of love.
Unfortunately, Hook has surrendered to the Darkness (and acts quirky as Rumplestiltskin when around Mr. Gold), continuing Nimue's plan to destroy light magic; he manages to open a portal to the Underworld, bringing back every Dark One between Nimue and Zoso. Luckily, Hook's love for Emma allows him to see that revenge is not the right path, allowing him to seal all the Dark Ones into Excalibur; rather than have Emma sacrifice herself, as she has family, Hook offers his own life, freeing her of the Darkness. With this, both the Darkness and Excalibur vanish into nothingness.
Unfortunately, Mr. Gold created a new Dark One's Dagger to absorb all the Dark Ones' magic making him even stronger than Emma.