Containment crew
Castiel's role was easy. All he had to do was stretch out his hand and let a portion of his grace hold the creature still.
But it was not that easy. He was unfamiliar with his target and so he had to play catch up. He could feel its defences shift and he had to battle to catch each new trick it offered.
It took more energy than he expected but he held firm. His hand shook with the effort.