Dark herald of Tzeentch
Highly intelligent and deadly, heralds of Tzeentch were often seen on the battlefields of the Stygian Wars. The ones often spotted during the Stygian Wars differed from your normal herald of Tzeentch thus earning the designation of dark heralds. They wore plate armor in alpha Legion colors and their staff had a vicious blade attached. They also tended to be bulkier and more geared to battle than regular heralds. They often appeared after a sacrifice had been performed subsuming the sacrificial victims body. On the battlefield they often summoned their daemonic kin and sought to wreck havoc on the mortal plan with a spitefulness that shocked those who witnessed it.
I have used a nephalim blood seer model from the Hordes line to represent a Dark Herald of Tzeentch. I simply added it to a smaller base.