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@LeeRoy Sorry for the late response)
D'Angelo had not been lying when he said that he didn't know who the old man was, history was not one of the assassins strong points. What he did know was that nobody carried a plethora of weapons if they didn't know how to use them. How efficient was this old man? That was the question that needed answering. D'Angelo's words and movement were calculated and planned, he wanted the old man to attack, he wanted an opening to see if he could end it in one stroke or if there was more to his opponent than what he appeared to be.
There was a flurry of action, everything happening in such a short span of time that if someone normal were to be looking upon the two they would no doubt miss the intricate and perfected motions that came into play. The old mans attack came as D'Angelo was turning affording him the chance to see as well as hear his opponents movement, the turn would end up becoming a side-long step to bring D'Angelo out of harms way by a couple feet.
As he stepped his left hand, the side facing his opponent, would throw a pellet straight down, the result being that the small alley would be covered in a thick dark grey smoke centered on D'Angelo and quickly expand thirty feet out in all directions. The vial in his right hand would be held for but a moment, giving the smoke time expand then it to would be thrown, a flick of his wrist would send the alchemist fire low, about waist level, and directly at where the old man had been standing. If it hit than the old man would find himself engulfed by a flash-fire that while not lethal, would be painful but brief unless there was something on his person that could catch fire. If it missed it would likely hit the ground with a brief flash of light and heat, doing nothing more than leaving a black mark on the stone streets.
Regardless of the results D'Angelos left hand would pull the gnomish lens device he wore over his eyes and flick it to a red lens. In that same moment, D'Angelo would leap up and backwards, towards the wall behind him, his feet would find easy purchase roughly eight feet above the ground, all thanks to a magical device he wore in his left boot. What's more is that unless his opponent had some way of hiding himself the red lens would show D'Angelo his opponents body heat and allow him to plan his next attack accordingly.