Kiss of Mephisto
From Diablo Wiki
The item originally appeared as a giant, black gemstone embedded in a triangular column of red-streaked marble. Due to its deep red complexion, it's also called the Blood Marble.
The Kiss of Mephisto was kept in a cave underneath the temple of the Triune, along with the band of Morlu. The Blood Marble would continuously revive any Morlu who fell as they battled with eternal bloodlust in the cavern. This gave the Morlu continous battle experience, becoming the most elite of demonic soldiers.
Malic describes it as following: The kiss of mephisto let out a burst of black light. Not darkness, but completely utterly black light.
The artefact was destroyed by Uldyssian, fighting his way through the cavern. With the destruction of the stone, the threat of the Morlu was gone as well.