Horn of beckoning death

Beckoning death was a mighty spell used by the lich Szass Tam, Zulkir of Necromancy, to turn mass numbers of people into his undead servants.

Components
A key component of the beckoning death was a mysterious red horn with a curved shape and an uneven mouth that was engraved and bound in metal as if fashioned into a drinking horn, and which glowed from within. It's unknown what it was called, what powers it had of its own, and what fell creature it came off.

Effects
The beckoning death was a spell that was unspeakably unholy and described as "the greatest evil the world has ever known."

When raised aloft, the horn would draw down from the sky crimson strands that appeared much like fresh blood before turning dark. These would channel through the mouth of the horn, which would then spew red smoke from its point. This consumed the souls of all those caught within, swiftly transforming them into undead creatures under the control of the horn's bearer.

The spell could affect vast numbers of people, even the populations of whole cities.

A Curious Precursor
While the Harpers were distracted with the Harpstar Wars in the late 12 and early 13 centuries DR, the corrupt and ambitious Harper Rundorl Moonsklan happened to meet Szass Tam, a Red Wizard of Thay, who was by then the Zulkir of Necromancy and a lich. With Rundorl desiring to be 'a Harper King' and the power behind every throne in the North and Szass scheming to destroy his rivals in Thay, the two made a dark deal: Szass would funnel Rundorl information on his rivals and Rundorl would gain prestige by sending Harpers to win victories over them.

To justify this focus on Thay, a land previously neglected by the Harpers, Rundorl spread the story of "the spell of Undeath". According to information he'd 'discovered', the Red Wizards were developing a new spell capable of instantly turning the populations of whole cities into undead slaves in order to quickly produce armies and threaten and enslave all of Faerûn. According to Rundorl, the Red Wizards were yet to perfect a way of protecting themselves from "the spell of Undeath", especially when cast by a rival, and experiments were naturally difficult to conduct. The only things stopping them were these issues—and the Harpers.

The plan went perfectly and Rundorl sent his fellows into battle against those Red Wizards and even zulkirs whom he claimed had involvement in "the spell of Undeath" and both he and Tam advanced in power. Eventually, though, Rundorl realized more Harpers were dying than Thayans and his exhausted men were being assassinated and reanimated as undead themselves, and he rightly suspected that Tam had betrayed him. He broke off the alliance, then got into worse troubles.

And Szass Tam would go on to do exactly what the Harpers had feared...

Szass's Surprise
As Xenk Yendar would recall, when he was a boy in the mid-1370s DR, Szass Tam called all the other zulkirs and all the people of the Thaymount tharch, Xenk and his parents among them, to a grand celebration atop the Citadel. But it was all a lie—instead, Szass interrupted Zulkir Dmitra Flass as she addressed the crowd and produced the red horn from under his robes. With it, he cast the spell of beckoning death, thereby creating an army of undead under his control for his following conquest of Thay. All who tried to flee were slain by Red Wizards in his service, such as Sofina. Xenk saw a girl his age, Ishira, standing alone and lost in the panic. In their fear, Xenk's parents tried to force their son into the ritual, but he refused and fled, but the mark of Szass Tam on his head glowed with a magical connection. He escaped, but only barely, losing a part of himself to the beckoning death and left changed by the necromantic magic. From then on, he would age slowly.

Meanwhile, these undead would doubtless form the basis of the Dread Legions that Tam maintained for the defense of Thay in the 15 century DR.

At some point, however, the Harpers seem to have acquired or stolen the red horn, perhaps preventing Tam from casting the beckoning death. They stored it within the vault of Korinn's Keep, far from the lich's reach.

The Greatest Evil Unleashed
In the mid-1490s DR, ex-Harper turned thief Edgin Darvis led a band of thieves, including Holga Kilgore, Simon Aumar, Forge Fitzwilliam, and Sofina, to Korinn's Keep to steal its treasures. However, Sofina betrayed the thieves and escaped with her prize—the red horn of Szass Tam's beckoning death.

Two years later, Sofina would be revealed as a Red Wizard of Thay and servant of Szass Tam. She used the red horn and cast the beckoning death over the Neverwinter arena for an attempted attack on Neverwinter.