Quick shot with a shotgun, most bladedancers spam the melee button, as soon as he is about to strike I run towards him and melee him, it works because I make sure I hit them at the exact moment after they strike, so I have a fraction of a second before they can strike again. Sounds kinda complex and unrealistic but it works great, and it's easy when you get used to it. Backstab helps because it's glitched and if you jump from the front it still counts as a backstab :P (Deals more damage btw)