This DLC contains the hero attire: Raven Doctor.

Plague Doctors wear a terrifying garb intended to keep them safe from miasma and bad humours while they conduct the grim work of treating the sick. The beak is stuffed with flowers and herbs to suppress the odour of putrefaction, and the robes are meant to keep infectious blood and matter off the wearer's skin.

Note: This DLC contains a hero attire which only changes the wearer's appearance, not their attributes.
The above DLC can be claimed by talking to the Town Crier in a capital or the Trade Colonies after purchase.