Warped and evil creatures living in and created by the Desolation.
In the wake of the purification of the Vileflow and the return of the Elves, the corruption of the Desolation has begun to reverse. Numbers of the Curst are falling off, therefore, although the trend is toward disappearance of the weaker breeds and concentration of the stronger ones as the borders of their "natural" habitat recede.
Further investigation of the magics used to create the Desolation - and by extension, the Curst - has shown that they are at least partially Fiendish in nature.
Over the years since the Slaying, the shrinking of the Desolation has brought the race of Slitheren to the notice of the rest of the world, as the versatile ratmen emerge as victors in the struggle for survival.