Song of Sadness
The following was learned via Salazaar’s use of the spell Legend Lore.
Use of the gate enables the opening of a gateway to other planes. Under normal use, it acts as a gate spell, allowing a precise location to be specified when the portal to another plane is open.
However, one can also use the cube to banish creatures to one of the planes, as in the spell plane shift, which banishes them to a random location within that plane. (DC 17 cha save)
Untold ages ago, the Cubic Gate was created by Aureon, the god of law and knowledge. Aureon gave the Cube to his daughter, Mesilliana. Mesilliana treasured the Cube, and used it to further her knowledge of the multiverse. At that time, the cube was able to open portals to any plane.
After a time, The Traveler, one of the Dark Six, learned about this artifact and of the great potential it held. Carefully, the Traveler planned and executed a plot to take it as his own. Catching Mesilliana off guard and alone, the Traveler was able to claim his prize, but in the process killed Mesilliana.
With his new artifact, the Traveler began sowing chaos throughout the multiverse, sending minions to every plane and leaving no corner safe to hide in.
Much of the time since its use by the Traveler the Cube has laid dormant, but at some point it fell into the hands of Iggwilv, before it was passed on to Strahd von Zarovich.