Shade

"The old legends do speak of such creatures. They call them "shades". Poor, tormented souls summoned from their rest by the necromancer's art."

- Gaius A Shade is a resurrected soul pulled from its rest by a necromancer. The shade possesses its former body and skills and recalls their original name, but it is in essence no more than a mere shadow of their mortal self. A shade is also resistant to attacks by magic. They are also under the necromancer’s power and may be moulded to their will, with this control lasting until the shade is once again killed and the soul released.

Morgana, High Priestess of the Triple Goddess, sought the advice of the Dochraid to raise a shade with a magical coin given to her by her sister Morgause. The Dochraid told her to travel to the last of the five Gateways that separate the living world from the world of the dead. Morgana went to the Pool of Nemhain and cast the coin into the lake’s depths, forcing Sir Lancelot’s spirit into the living world.

Morgana used the shade of Lancelot to come between Arthur and Gwen, who were preparing to get married. Lancelot succeeded with the help of an enchanted bracelet, and Gwen was banished from Camelot. Under Morgana ’s orders, the shade of Lancelot then killed himself and Merlin was able to free his soul with the spell "Grið fæstne mid þisse tintregian sawle", allowing him to rest peacefully (Lancelot du Lac).

Myth
In the myths, a shade is the spirit or ghost of a dead person from the underworld. It can be called to the world of the living by dark magic. They are wicked creatures that wreck havoc in the human world. Although Lancelot did cause Gwen's exile, he can't be described as evil due to the fact that he didn't have his own will.