Life-Stealer

Originally carried by Artemis Entreri, a cut character in Bodhi's Lair in chapter six, this powerful dagger can later be brought in The Black Pits II tier 4 store.

In-game description
"This dagger weighs heavily in your hand and is warm to the touch. Merely having it on your person makes you feel uneasy for some reason. The gem mounted in the hilt seems to have an inner light of some sort, though how it can have such illumination and still be so deathly black at its core, you do not know."