Meet Gnarlag Prosgino von Biggus Esq. and David
Gnarlag is a creature possessing the power to take any humanoid shape or form and chose to be a peddler of medications, tinctures and alcohols of less than benevolent type.
In a apparently chance meeting with an eager buyer, he found himself in the service of a crime lord beholder that goes by the name Don Squigglione that answers only to an eldritch god.
Gnarlag now wanders the world, emboldened with power granted by Y'golonac and travelling with a gazer familiar named David, finding new regions to spread the corruptive force of his patron or risk disappointing his deity. His usual methods see him roll into town, sell as much of his wares as possible and then ducking out again, usually in the cover of night, before the rotten fruits of his efforts set seed.
Hearing of a land that has been effectively cut off from healthy outside trade, he has travelled to Barovia with a cart load of merchandise and the hopes of setting down roots for Y'golonac in fertile soils.
What he has found is the reason why there isn't a good trade route with Barovia and that he is effectively as stuck within the countries borders as the rest of the civilians, And now he is trapped, face to face with the longer term effects of his efforts, unable to escape until he, and the odd band of adventurers he has alighted himself with, take down the vampire Lord Strahd and break the barriers around the land.
You can find Gnarlag's DnDBeyond character sheet Here