"Insolent little wretch; restrain that harpy!" The other cultist shouted angrily, clearly not a fan of having the ritual interrupted. Sevarian slowly turned towards Kathlin who was hanging on the wall, and raised his hand. Suddenly, a dark presence surged over her, dropping her body temperature by what felt like multiple degrees and pulling the breath right out of her lungs!

The shield which had protected the troll was dispelled, and Sevarian slowly shook his head at the little girl trapped to the wall.

"Like a fly before the storm." He commented with a calm tone, not sharing the same passion as that of his infuriated underlings.
"Impressive effort, but it is worth nothing. You have to learn that there are some things that simply cannot be stopped. Some things, are simply meant to be, regardless what you might do to avoid it. And in it all, death is the only certainty."

Sevarian turned away from Kathlin, leaving whatever curse he had cast on her in place as he casually walked over to the summoning circle with the cultists surrounding the troll. Stopping next to the creature, he looked down at the troll.

"I will give you a purpose far greater than anything your little tribe could ever have offered you. You will touch power beyond anything you could ever imagine. It will course through you. And it will rip you apart."

As the the troll raised his head to look up at Sevarian from where he stood on his knees, Sevarian suddenly jabbed his right hand forward; having secretly taken the knife from the cultist! With little warning, he buried the knife into the right side of the troll's throat; holding onto one of its long tusks to keep the creature still as he sliced with grateful motion from one side to the other of the troll's throat with his knife.

" ... a sacrifice of blood and bone, to serve as a conduit for our power... "

As he retreated his blade, blood gushed forward from the gaping wound in the troll's throat. Standing back, Sevarian let the Troll clutch his throat as the blood flowed down onto the floor beneath him, raining down into the runic symbols that had been etched into the ground around him. As the blood touched with the runic scriptures, they suddenly reacted; glowing ever more intensely in a ghostly blue light as they seemed to absorb the blood from the troll.

Meanwhile, the rest of the cultists had gathered in a circle around them. As the blood of the troll quickly left his body, they raised their hands in unison. When the troll was about to collapse, his body suddenly stiffened. Its gaze turned blank, and suddenly the body floated up to its feet. Even as the entirety of its chest had been painted red by the gushing wound in his throat, the body still stood; as if it was being animated by invisible strings! Opening his mouth, he screamed in anguish, his voice sounding more like a distorted echo drawn from his very soul as he had no breath remaining to physically scream with!

As the gruesome ritual continued, the runic markings that had been painted on the remainder of the trolls above their own tribal tattoos suddenly began to glow. Within seconds, all of them succumbed to theirs knees, screaming out loud as if the runic symbols on their bodies were burning their very flesh! 
As they languished in anguish on the ground, they began to be dragged across the floor towards the animated troll in the center of the summoning circle by invisible hands. As the cultists around the ritual circle began to chant in a darker tongue, the suffering trolls were lifted up into the air around the circle.

The blue light that had emanated from the runes at the start now illuminated the entire room in a bright blue hue, pulsing with power as the screams of the main sacrifice only increased in magnitude! 
Watching the ritual, Sevarian turned to look back at Kathlin on the wall.

"Some scholars say that ever since mortals pervaded the world, they have ravaged and squandered the great powers within it, making it more and more mundane beneath their feet. But the Scourge taught me differently. Just like mortals use magic, they themselves can be fuel for magic. With the... proper ingredients, simple practitioners can create spells far greater than anything even the highest of circle mages in Dalaran ever could. The power in the world never faded. It simply took another form, and now I am showing you how to extract it."