Curse of Strahd
An amber sarcophagus looks like a rough block of solid amber 8 feet tall, 5 feet wide, and 5 feet thick. Trapped inside the block is a sliver or wisp of utter darkness no more than a foot long. The darkness is the vestige of a dead and hateful god-a shard of pure evil with shreds of sentience and awareness. The vestige can’t be harmed or controlled, and it is immune to all conditions.