The Hollowed One

Background
Vibaem was a rival of Janak, within Candlekeep, THE library of Faerun. Maximilian and Vibaem actually had classes together, Max being his understudy, however it was alluded that he was probably in disguise at the time.

It was revealed eventually that Vibaem was working for the Demon Worshipper Parthinia Quell. Upon defeating Janak upon discovery and turning him into a different version of a human, before again transforming him into a chicken, Vibaem stole many books, including one on Barovia and others on Demon Worshipping.

He eventually had Tormund Tallowhill working for him to bring him children from an orphanage in Westbridge to him.

Interactions With Mystic Obscura
Vibaem somehow had part of him locked within a staff, that came into Myastan Balasar's possession. Upon influencing Balasar to kill a member of The Arcane Brotherhood, Mystic Obscura destroyed the staff, and Vibaem latched himself onto Balasar. It is unknown whether this form of Vibaem is the main form, or just some part of him.

Vibaem threatened to kill anyone Balasar revealed his secret (that Vibaem was attached to him) too. When Bird threatened Balasar, Vibaem appeared and threatened the Fae himself. The two fought for a while, before Bird vanishing. Vibaem explained to Balasar he wasn't always with him, and asked for the name of the Man they had gone to save at Summervale Farm. Balasar refused to give the information, leaving Vibaem frustrated with his inability to pierce Balasar's mind.

Vibaem eventually contacted Balasar again, when he heard the group were planning to head to Candlekeep, however, Vibaem warned him he'd hurt his friends if Balasar didn't stop them. After failing to convince the group, Balasar was confronted by Arannis. Vibaem took over and turned the elf to stone, before revealing himself to be inside of Balasar to the rest of the group.

Vibaem was strangely quiet when Mystic Obscura headed to Last Light to get help. He did, however, attempt to intervene when the Unicorn Kaisa attempted to banish him, only to be stopped by the cured Arannis, who blocked his spell and allowed Kaisa to vanquish Vibaem into Balasar's cape, rather than him.