Ring of Exalted Marrow Ring

Gazing through this ring, you find that there is no other side, only a small sucking blackness that defies explanation.

Exhort the Risen: Flavour spell text for Control Undead.
Ghoulish Touch: Lash out with deadly claws and possibly Paralyze the target. (2 turns.) This attack cannot paralyze Elves and Undead. Resets on a Long Rest.

Found in a chest atop of Moonrise Towers. You visit this location as part of the post-Nightsong content to get to the final stages of Act 2.