The blades of these assassins were lathered with poisonous oil, so once struck and the flesh comes in contact with this poison, it would ensure that the victim would suffer, as for death?
That was rare to happen, a poison that could end a Knight was hard to come by. So most just use common mortal poison and use it to weaken their enemies at most. Which would earn them an edge during an assassination in case things go awry. Which they have at this point.
"It stin..gs," Farhad said, while his exposed head flared with yellow flames. Making him look like a hellspawn. The pain and lethargy he should have felt from the poison was nothing in front of the pain he currently fell under the sunlight, which was trying its best to kill him.