The thing chasing the Vasari
A very powerfull old psychic race with their own sense of judgement, police of the universe as you will,
Destroying races that become too powerfull and cant use their power responsibly, thats why the vasari are being chased,
Hence it explains why the advents psyhic powers, they are just starting where the older race has all the knowlegde about,
their strong psychic power drove the remaining vasari insane and now they are destroying any vasari technology so the lesser races couldnt make use of it (hence the spreading darkness).
They are comming for the vasari, and for the other races, because they have to pay for their "sins".