Dark One's Dagger

The Dark One's Dagger is an object featured in Once Upon a Time in Middle-Earth, originating from Once Upon a Time.

Background
Nimue, the once lover of Merlin, destroys the sword, Excalibur's tip so Merlin won't cut away her immortality. In order to control the Darkness, Merlin tethers Nimue's name to what becomes the Dark One's Dagger.

Trivia

 * Apparently, there can be more than one Dark One, as Bilbo's name appears on one side and Emma's appears on the other side.
 * However, this is only because Emma and Bilbo split up the Darkness
 * The Dark One's dagger is an allusion to the fact that in the original fairytale, "Rumpelstiltskin", where the Miller's daughter