As this game will never see the light of day, I will explain the story as I like closure, even if an imperfect one. It was based upon the adventure The God that Crawls that uses Lamentations of the Flame Princess system. It had the same principles: one mystery; a huge labyrinth; and one major monster, literally unkillable. But with some differences: (1) other monsters, mostly to provide tempo battles against the incoming major monster; (2) many traps varying from common ones to really devious mortal traps; (3) cursed items, but instead of bad items, they are good ones with some kind of disadvantage; and (4) some fixes from what I found bad about the original adventure.
Below is the summary I wrote for the game (translated from Portuguese):
The city of Khandora is a small town embedded in a virtually uninhabited plain located far from major local shopping centers. A town of ancient origin being located 20 miles from the main gate of commercial, usually forgotten by all. This city has never been important politically, geographically or commercially. The only really important fact of this city throughout its existence was used as a place of birth for a major hero, the famous champion Darius McGray. A really important figure in his time, unblemished honor figure, his name immortalized in stories and legends, winner of numerous important battles and admittedly savior of kingdoms in more than one opportunity.
Darius McGray, however, shortly after his birth left his city of birth to become the great hero who became, staying a long time away. But he never forgot his hometown while alive, and so felt unable to continue his life of adventure decided to return to finish his days in his hometown. God in his favor during the decades in which the champion remained in service, however had other plans for his championship.
This God, who had greatly blessed paladin's abilities to something far beyond a mere human, something he alone already was decided to bless you with a survival and extra toughness, defiance of the will of Darius McGray. This received the extra gifts, without noticing them or change his decision to retire.
God just forget it over time and going to look for another champion for their cause after a few years. And Darius McGray ended up living in peace over the years until for a quiet night trying to protect their city he was bitten by a werewolf kind of mutant created by the crazed wizard experiments in some remote corner of the kingdom.
The werewolf was killed in combat, but his curse corrupted the famous hero. The mutant curse of the werewolf combined with the powerful blessings of God upon the paladin did not have a good result. Realizing the danger that would become and not being able to suicide without destroying his soul, Darius McGray as last selfless act of his life made an unbreakable vow never to leave the labyrinth built in his hometown to protect the spoils he had acquired during his long career on the side of justice.
Soon his mind was consumed by the curse and his body was completely revamped to create the most dangerous werewolf of all time. A mass of muscles almost a ton of weight, highly lethal and deformed even to the harmful patterns of a werewolf usually the worst and virtually indestructible.
Centuries have passed since then, the famous hero nothing left, just a dangerous monster that is revered as a true god in his hometown. A monster that even today continues to wander inside the maze created and that over time began to generate a negative influence on all the inhabitants of the city.
A little cheesy, I know, but an improvement over the original and most of this information would be provided in small parts or never learned depending of the path of the adventurers.
The game was 40 to 60% concluded.