The Skarreth dynasty was once great and powerful and its nobility fancied themselves as warrior scholars and patrons of the arcanoscientific lores without equal. As a demonstration of his near limitless power and wealth their Phaeron, Ozymandias III, ordered the construction of the greatest repository of knowledge the universe had ever seen or ever would see. This library would contain the sum total of all knowledge and scholars and crypteks would travel from the far reaches of the galaxy to view its archives and gaze in awe upon Ozymandias' greatest triumph.
Constructed deep within the heart of the Skarreth's crownworld of Silentium the library expanded to such a degree that the planet itself became a hollow shell containing the library within. The corridors and halls were resplendent in black marble and trimmed in gold and scarlet, all surfaces were ostentatiously ornamented and the walls were filled with engraved reliefs of the most significant events in galactic history.
When the great sleep came the work was left unfinished and the Skarreth retired to their stasis tombs. As they slumbered they were powerless to act as their star went supernova, turning the surface into a sterile desert of obsidian glass and stripping the planet of its atmosphere. Left barren of even the smallest microbial life the planet was cast adrift in space to forever wander as a rogue planet unlit by any star.
The Necrons of the Skarreth dynasty survived the devastation, protected as they were by their stasis tombs constructed inside hyperspatial oubliettes buried deep beneath the planet's crust, but the damage to the tomb complexes systems was catastrophic. The planet spanning artificial intelligence at the core of the library was driven insane by data corruption and became trapped in an eternal loop of defragmentation and glitching subroutines. The personality engrams of the sleeping Necrons were likewise corrupted. On awakening even the highest ranking of the nobles were afflicted by amnesia, bouts of madness and mania, violent ticks and spasms and widespread kleptomania coupled with deeply obsessive and irrational behaviour.
Utterly insane the Necrons of the Skarreth dynasty are sure of only one thing, an overriding imperative encoded into them by the planetary AI to finish Ozymandias' great work. Unfettered by rationality this all consuming obsession leaves the nobility of the Skarreth unable to see the impossibility and hubris of their task. The library itself lies in ruins with vast continent sized tracts of galleries cut off by collapsed passageways, left abandoned and unpowered to be covered by the dust of aeons. The tesseract architecture used to give the library near infinite capacity is broken beyond repair. Entire sections of the library slip between dimensions, their layout a tortured labyrinth of contorted non-euclidean geometry. To wander through such damaged areas is to risk being ripped apart by a hyperspatial shift or to become trapped in an obscure dungeon dimension. It is even said that it is possible to become displaced in time and find oneself lost in a section of the library that hasn't been built yet.
The cascading failure of the library's tesseract architecture extended to the the hyperspatial oubliettes housing the tomb world's stasis chambers. Soaked in the chaotic energies whilst they slept the legions of the Skarreth dynasty are forever cursed to phase between dimensions, never wholley in sync with the material universe around them. To onlookers they appear to shift in and out of existence and be riven by bouts of uncontrolled visual static. Weapons blasts and blade thrusts sometimes pass straight through them as if the Necrons are just an optical illusion. Most terrifying of all is the way the legions of the Skarreth dynasty move. They march forward in the slow, ponderous manner typical of all Necrons but if an observer should blink or look away for even an instant the horrific forms of the Necrons suddenly appear much closer. This tests the sanity of the Skarreth's opponents and leads to enemy soldiers gazing at the oncoming tide of undeath in wide eyed terror, desperately trying not to blink. Nobody ever sees the instant when the Necron tide suddenly phases forward, even if onlookers ensure that someone keeps their gaze upon their adversaries at all times.
The Crypteks of the Skarreth have learnt to control this dimensional instability and cloak themselves in it, appearing as tortured spirits. Jealous of the precious contents of the library they employ the ghostly forms of the Sentinels to protect it. These wraith like beings have been left completely insane by the madness afflicting the Skarreth and replace their forearms with lethal monomolecular blades. They haunt the corridors and chambers of the library, suddenly materialising from the smallest patch of shadow to slay any intruder incautious enough to make a sound louder than a whisper.
Now fully awakened from their millennia long slumber the legions of the Skarreth dynasty hunt the length and breadth of the galaxy and employ any means in order to obsessively collect knowledge and secure it in their library, regardless of how profound of trivial that knowledge might be. The Skarreth dynasty have exterminated entire alien civilisations in order to ensure their knowledge is collected and forever preserved within the library.
The library is said to contain items as diverse as the shipping manifests of Myrenthis II, the last surviving copy of Shakespear's complete works, the only entirely accurate equation describing the material universe and entire Inquisitorial archives of forbidden texts. The Skarreth also seek physical artifacts and specimens to illustrate this knowledge or to be deconstructed for study and analysis. One chamber housing texts on selective breading contains a live specimen of every species of grox used in Imperial agriculture, whilst another housing texts on Imperial gothic architecture contains a cathedral stolen for the purpose of providing a practical example of the application of this knowledge.
The actions of the Skarreth dynasty are totally unpredictable and often without any reason comprehensible by a rational mind. This trait has made them unpopular allies with other Necron dynasties who find it impossible fathom their goals and motivations. The Skarreth dynasty also prize the knowledge and artefacts of the superior Necron race above all others, leading to frequent instances where light fingered Skarreth nobles have made off with the most valuable possessions of the other dynasties.