When you come into a room that has fifty goblins and one tall, thin human in black robes holding a staff swathed in dim green light, the human is probably the BigBad.
Or maybe it turns out that the evil human guy was just one of many minions working for a vampire with plans to rule a kingdom. Well, then the vampire is the BigBad.
Unless the vampire is a scheming servant of an ancient dragon who plans to reduce most of the world to charred and smoking cinders. In which case, yeah, the dragon is the BigBad.
But the dragon could be working for some dark god bent on wracking the very universe to its breaking point and unleashing some hellish antiexistence upon us all. Well, then...
Or, screw it, just assume that it's the Ta'bar'pur.