In Curse Of Strahd, Vaund's sarcophagus was encountered by the Heralds of Dawn, and contained barely any power. They had no ability to contact the adventurers as they had recently used their abilities on Jassarian, and had failed to get them to break their prison.
An ageless Dark Power native to the Plane of Shadow, Vaund was once a higher being who preyed on souls within the veil of the Deepmists. In the Pre-Unified Age, they were locked into an amber sarcophagus by high mages of the Azure Paragon, then were stored in the Amber Temple alongside other Dark Powers. Claiming the title "The Evasive," Vaund asserted to have ultimate power of avoiding divinatory detection, but were only able to influence the realm beyond their tomb with minor magic.
As their powers waxed and waned during the Barovian Calender Timeline, they contacted adventurers to harvest soul energy from Barovians. Like all Dark Powers, they had methods of feasting on souls departing mortal's bodies, and in exchange for magical power, would request that their champions destroy their sarcophagus. However, they experienced few successes, as souls leaving Barovia were nearly always consumed by Vampyr, and their champions were killed by the many horrors of the valley.
Vaund made contact with Jassarian Sala-zan, and helped guide him and his party to the Amber Temple while shielding him from the watchful eyes of Strahd von Zarovich. However, the Dark Power's effort ultimately failed, as Jassarian was killed by three Flameskulls after accidentally awakening an Amber Golem.