Eldritch Omens: A 9th Level Adventure for 5th Edition

Long ago, there lived a group of merfolk who worshipped an all but forgotten eldritch deity. The being from The Realm Beyond granted them great power, but at the cost of their sanity. Eventually, the merfolk summoned forth the being's avatar, an aboleth named Zzak'zara. The creature promptly enslaved the merfolk and tried to bend them to its will. The merfolk, however, were too weak to withstand its psychic onslaught and were slain instantly. Unfortunately for Zzak'zara, it was now trapped in a cave beneath the surface with no way to escape. Centuries passed and the creature slowly went mad from isolation becoming a shadow of its former self. Now, the creature has become an Abolor, a vengeful, predatory monster that seeks only to devour and spread its madness.

With its caretakers dead or scattered to the far seas, the temple of the merfolk fell into disrepair, as did their outposts on the surface. Over time, others came to occupy these spaces and things would have remained peaceful if not for the curiosity of a group of sailors who found one of the aforementioned outposts. This small band of pirates setup camp within the hollowed out ruin and planned on using it as a staging point for their raids. Unfortunately, one of them plumbed too deep and, fell under the sway of Zzak'zara who mutated him and his crew into fish monsters. Now, these eldritch abominations seek out others to bring to their master, kidnapping passing ships and raiding the local shores. If nothing is done, soon the Abolor will have an army of insane fish cultists worshipping it deep beneath the waves.