hi i was playing through watchers keep with IA for the first time and found only the mage part of the essence and the blood.is the other half found somewhere else or is there some other boss i have to kill other than demon prince and the ancient dragon

I found the Barbarian essence guarded by some bosses in another area that's available in Ch. 2. But IA's randomization of treasures could mean that it's somewhere else in your game.