Cordial of Tzeentch

The Cordial of Tzeentch is made from water in which the ground remains of a feather or claw from a Lord of Change is dissolved. Only Daemons and Chaos Sorcerers of Tzeentch are capable of making this brew. Needless to say, vials of this substance are incredibly rare and highly treasured by followers of Tzeentch. The Cordial’s physical properties change non-stop, and it has no consistent colour, scent, or viscosity.

Possessing the Cordial of Tzeentch is a high crime, and owning it carries a death sentence, although Wizards strive to save these rare items to study rather than see them cast into cleansing fire.

Source

 * Warhammer Fantasy RPG 2nd ED -- Tome of Corruption (pg. 89).