Teine Diaga

"The ritual used the mandrake root to bring unimaginable terror to the victim. Their screams could be heard twenty leagues away. When it was finally over, their will was no longer their own."

- Gaius to Merlin

The Teine Diaga is a powerful magic ritual that uses the mandrake root to bring unimaginable terror to its victim. When it is over, their spirit has been consumed and their will is no longer their own.

This spell can only be reversed by summoning the White Goddess at the Cauldron of Arianrhod. The victim must enter its waters willingly; if they are forced or tricked in any way, their soul will be lost forever.

History
When Gwen was kidnapped by Morgana, she was taken to the Dark Tower and imprisoned in a room filled with Mandrake Roots. The roots were coated with a black potion and induced nightmarish hallucinations of endless screaming and her friends and loved ones laughing at her.

Morgana visited at regular intervals to offer comfort and try to convince Gwen that she was only person she could trust. She resisted at first, but her resolve slowly crumbled at the hallucinations intensified. By the time Arthur and his men rescued her, Gwen's spirit had been consumed and her mind was under Morgana's control (The Dark Tower).

Under the influence of this enchantment, Gwen gave the outward appearance of being very placid and sweet. Inside, however, she cared for and believed only what Morgana told her to. She loathed her former friends and murdered Tyr Seward without batting an eye.

Gwen made multiple attempts to assassinate Arthur during this time. She nearly succeeded in poisoning him and framing Merlin for the crime, but Merlin managed to escape from his cell and heal him. Later, when Gwen recruited Sarrum of Amata to assassinate Arthur during a treaty signing, Merlin again intervened and Sarrum was killed instead (A Lesson in Vengeance, The Hollow Queen).

When Merlin finally convinced Arthur of Gwen's enchantment, he went to the Dochraid to find out how to cure her. He learned that the only way to free her was to summon the White Goddess at the Cauldron of Arianrhod.

Merlin and Arthur conspired with Gaius to drug Gwen and take her to the Cauldron. Once there, Arthur persuaded her to enter its waters and Merlin (disguised as a sorceress called the Dolma) used his magic to summon the White Goddess, breaking the enchantment and restoring Gwen to her true self (With All My Heart).

Appearances

 * Series 5
 * The Dark Tower
 * A Lesson in Vengeance
 * The Hollow Queen
 * With All My Heart

Trivia

 * Though Morgause once stated that only those with magic could hear the mandrake root's cries, Gwen was able to hear their screams as part of her torment (The Dark Tower).
 * According to Gaius, the screams of the Teine Diaga's victims could be heard twenty leagues away (With All My Heart).
 * Before the Great Purge, this ritual was primarily used by High Priestesses, who used its victims as slaves for all eternity (With All My Heart).