The Changeling

No one knows the Changeling's true form; the oldest grimoires suggest that by now not even the Changeling does. It is mimicry elevated past art into predation: not a disguise worn over a daemon, but a daemon that has misplaced itself among its disguises. It has been generals, matriarchs, oracles, and beloved local saints, and its performances are flawless down to the scars, the childhood songs, and the small kindnesses its victims were known for.

Its sabotage is patient and surgical. A garrison commander reorders the watch-rotation one fateful night; a high priest blesses a fleet with words one syllable wrong; a peace-broker smiles at precisely the wrong moment, and provinces burn for a generation. Often the Changeling is gone long before the catastrophe flowers, and the worst of the damage is done afterwards by the survivors: cities that tear themselves apart hunting a daemon that may never have been there at all. That paranoia is not a side effect. It is the point.

Even the legions of Chaos treat it with wary courtesy, for the Changeling recognizes no rank and spares no dignity; it has worn the faces of warlords to squander their armies and of daemon-princes to settle wagers only it understood. Tzeentch prizes it as a favourite instrument, while remembering, presumably better than anyone, that a favourite face is exactly what the Trickster most likes to borrow.