Bearing Ancient Scars
Perhaps foremost among the unfound oddities of the universe is the one charmingly named the Omphalocelic Scab.
Known about from the legends of those who are themselves legends - and bearing in mind that all translations from the Precursor are, at best, deeply approximate - we are told that there exists an imperfectly healed scar in the fabric of the universe itself. This scar came about, the legend says, because in the aeons of deep time there existed a group both sufficiently powerful to command the necessary ontotechnology, and sufficiently dedicated to the cause of anarchy to make use of it to repeal all laws.
All laws.
If the story is to be believed, after casually disposing of the merely social and ethical, they had successfully abolished the physical and had turned upon the metaphysical and mathematical before the inevitable local eschatonic collapse and eruption of cacoastrum rendered their Infernal Device no longer in any condition to unmake anything.
Is the story to be believed?
Well, it is taken seriously enough that various groups interested in preventing the utter annihilation of everything at the hands of the Bloody Stupid are actively searching for the Omphalocelic Scab and anything that may remain of its creators. Many locations have been proposed - for the most part, anomalous nebulae, voids, and remnants, although it has also been suggested that the Flotsamic Shore's odd wealth of strange treasures and neverweres may be the lingering aftereffects of such a reality excursion.
...but translations from the Precursor are deeply approximate, and so it could be nothing more than myth. A child's cautionary tale, warning against playing with dangerous toys.