if you want to know how to land a black flash perfectly with vessel you're in the right place. so first to land a black flash you need to press the button after one second of pressing it like a double press .like that. others say that you gotta press it after you characters moves his arm and thats incorrect. to land a chain of black flashes you gotta go behind the player. and start pressing the button like four times in the row .and and you can do a black flash finisher by pressing the button w