The Blue Scribes
The Blue Scrubz, otherwise known as Xirat'p and P'tarix (yep, their names are just reversed) are a pair of Blue Horrors in the service of Tzeentch.
Tzeentch has tasked them with discovering every last spell and piece of forbidden knowledge there is to know, in an attempt to boost his own power and rise to the top of the Great Game. However, wary of what might happen if someone else got their hands on this information, or the pair began letting all this knowledge get to their head, he put a safeguard in place. P'tarix is able to use runes and glyphs to record spells, but can't read so has no idea what he's writing. Xirat'p can read the spells his brother writes, but has no idea what spell it actually is. Presumably this leads to Three Stooges-esque arguments at every opportunity.
On the Tabletop
Filling the category of Tzeentch's unique Herald alongside the Changeling, the Blue Scribes are a HQ unit for Chaos Daemons. This is your anti psyker unit, but at short range 12" don't expect them to live long unprotected. In the enemy psychic phase the opponent will take -1 to their psychic test and if the enemy fails a test that power is siphoned. With a power siphoned they get to use smite but not as a cast so it cannot be denied and it counts as the minimal needed to cast. On each turn during the psychic phase, pick a psychic table and roll a d6, auto-manifesting that power with no warp charges expended.