Ziggurat sphere

Ziggurat spheres, also called siphons or spinning orbs of death, are artifacts of the Age of Arcanum that were used to funnel magic energy into the Shadowfell to revive Vecna. Two spheres were encountered by Vox Machina: one beneath Whitestone and one in the Smouldercrown Mountains of Marquet. A third sphere exists somewhere unknown in Exandria. Each siphons is paired with a twin, and these twin spheres act as portals to one another.

Siphon is indirectly related to a Sphere of Annihilation; the enchantment on the siphon is an "off-shoot" of the enchantment on a Sphere of Annihilation.

Appearance
The orb is a small, onyx-black sphere, about the size of a dime or a marble, which hovers a little above the ground. On close inspection, it appears to be spinning very rapidly.

When manipulated by Delilah Briarwood using her amulet, the sphere turned bright white or white-gray in color. In a vision from Sarenrae, Pike saw this sphere as a doorway surrounded by spinning blades.

Properties
When activated in the ritual involving a blood sacrifice, the sphere siphons magical energy within a certain vicinity, suppressing their effects, and transferring this energy to another location. Magic items and expended spells have no effect within the siphon's radius, however, resume their magical effect once moved away from the sphere's influence.

Anything that touches the black orb is sucked in and takes force damage. However, by using a special amulet, the Remnants were able to safely travel through the ziggurat orbs to their twins of opposite color, in their case, located on the Shadowfell.

Also, the amulet is able to turn the sphere white, switching from absorbing state into allowing magic to come from the Shadowfell into the Prime Material.

History
Siphons were initial created to harness and shift large accumulations of ley energy but it was inconveniently placed, the magical spheres could be used to beneficially triangulate and shift the leylines.

During the Age of Arcanum, they were used as a prevention mechanism against powerful mages, which became more of a secondary with the start of the Calamity. With the ensuing war, siphons were used to craft many powerful magical items like Vestiges of the Divergence, which were thought to be mostly destroyed or turned inert at the end of the conflict.

Campaign 1: Vox Machina
Vox Machina chased Delilah Briarwood into the ziggurat beneath Whitestone, hoping to prevent her from completing some unknown ritual. Vex arrived in time to see Delilah complete a blood sacrifice, causing the orb to spin, then shrink to the size of a dime. Delilah believed that the ritual failed, but magic no longer worked in the vicinity. Once Delilah was subdued, Keyleth attempted to hit the orb with a piece of residuum. The piece was destroyed as it touched the orb, and Keyleth narrowly avoided having her hand sucked in, taking significant damage. The party then decided they were not equipped to deal with the orb.

They interrogated Cassandra de Rolo about it, but she was only able to say it was part of a ritual for the Whispered One, Vecna. Keeper Yennen offered to go look at the orb, and Vox Macina sent word to Eskil Ryndarien and Allura Vysoren to come investigate it as well. Gilmore said that this orb sounded like a Sphere of Annihilation. The anti-magical properties made it difficult to investigate, and Allura was only able to confirm it destroyed anything thrown into it. She hoped to bring her research to a library, but the Cobalt Reserve was recently destroyed. Eskil had little to add beyond that the orb appeared to be acting as a siphon.

After a salvage mission to the Cobalt Reserve, Allura reported that she, Gilmore, and Eskil discovered that the orb was not destroying objects but breaking them down to siphon their magical energy elsewhere, similar to siphons used during the Age of Arcanum. They determined the siphon must have another side, which may be on another Plane of Existence. No attempts to send scrying objects or other such items through the orb succeeded, and the researchers were running out of things to try without traveling to more places.

Subsequently, Vax'ildan used the orb's anti-magic field to escape the curse of a Robe of Flaying. The Chamber of Whitestone also began using the ziggurat as their war room, relying on the orb's anti-magic field to prevent illusion magic and Scrying.

In the course of further research, they threw more objects within the sphere, which Zahra Hydris described as a fun process. Nothing returned; this included a Pale Guard volunteer. There were no further volunteers. Vex'ahlia successfully shot an Oracle Arrow through the siphon, allowing her to see a twin orb at the other end (that was not producing an anti-magic field) in a broken, grey landscape with a black tower. Allura identified this as the Shadowfell and left for Vasselheim the next day to research the tower.

Lionel Gayheart approached Vox Machina in Whitestone to report a second orb in a ziggurat in Marquet. He also reported seeing members of the Remnants throwing "treasures" or animals, some of whom were still alive, into the siphon. Upon investigating the ziggurat, they discovered Delilah had been resurrected and that she could use an amulet to control the orb. When she turned the orb from black to white, its anti-magic field was gone. Eventually, she changed the orb to black again, and she and the Remnants stepped through it. Pike Trickfoot, through a vision from Sarenrae, saw the orb as a door into the Shadowfell surrounded by a hundred spinning razors. Using Speak with Dead, she further learned that the cultists' amulets allowed them to pass through the orb.

Donning the cultists' necklaces, Vox Machina passed through the sphere beneath Whitestone and arrived outside the city of Thar Amphala. There, they saw shattered objects from Allura, Eskil, and Gilmore's experiments. Vex'ahlia also saw a strand of ley energy reaching from the siphon to the Tower of Entropis at the center of Thar Amphala. She also saw two more strands from the tower down into other places across the city, implying that three spheres existed. Vax'ildan and Scanlan circled the tower to find where the strands from the siphons converged. Shortly after, the Remnants finished their ritual to return Vecna to physical form, causing these strands to burst with energy and fade.

The Legend of Vox Machina
The ziggurat sphere first appeared after Delilah attempted to summon Vecna, but seemingly failed, leaving only the sphere behind. After Delilah was defeated, Scanlan asked Yennen about the sphere. She responded that it likely had extraplanar connections, and that she had sent someone to investigate. A cut revealed that the man investigating it had been violently sucked into the sphere, but that Yennen was not yet aware that this had happened.