Tzeentch desired a catalogue of every spell that has ever been or will be cast, and in his wisdom he assigned the task to two of the least beings in his service. P'tarix can transcribe any incantation flawlessly but cannot read a word of it; Xirat'p can read anything but is incapable of writing it down. Lashed together atop a Disc of Tzeentch with quills, nets, and a toppling library of scrolls, they squabble their way across the Mortal Realms, and their bickering has laid waste to more than one battlefield when Xirat'p reads an unfamiliar scroll aloud just to see what happens.
The realms are generous hunting grounds. Since the Necroquake taught spells to slip their casters and stalk the realms as predators, the Scribes have hunted them like lepidopterists gone mad, netting living conflagrations and caging shrieking gravetides. Every capture is transcribed, argued over, occasionally set off by accident, and added to a collection that already rivals the libraries of gods.
The joke, of course, is on them. A finished catalogue would mean an end to novelty, and their master would sooner unmake the realms than close the last book; the Scribes were built incomplete precisely so the great work can never be done. Somewhere beneath the squabbling, both of them suspect it — and like every disciple of Tzeentch, they keep climbing anyway.