A night in the abyss
As a mad entomologist focused on nurturing poisonous insects¸ the Dark Powers of Ravenloft put great care in 'breeding' their cursed darklords. After a first phase in which they build an Island of Terror suitable to endlessly torture its prisoner¸ they also create harsh ordeals to test the 'subject' in order to determine if it deserves its 'title' and position. Sometimes those 'experiments' involve parties of adventurers kidnapped by the Mists and sent to destroy the darklord¸ as happened for example with Strahd in years 499 and 528. The Count eventually survived¸ gaining the 'privilege' of seeing his private hell expanding in what it would become Ravenloft Core¸ but not every darklord is so strong¸ cunning or desperate to overcome the Dark Powers tests. In that case¸ the heroes are allowed to come back home¸ the fledgling darklord is destroyed and the Island of Terror is re-absorbed in the disgusting¸ misty ectoplasm which forms the Demiplane of Dread. A night in the abyss is an adventure in which five 3rd level PCs are transplanted by the Mists in the dungeon in which a newly born darklord lurks¸ because the Dark Powers want to determine if he is 'worthy' of their 'attention'. Eagerly watching someone dying in the process¸ of course.