100% increased Damage while there is only one nearby Enemy
You take no Extra Damage from Critical Strikes while there is only one nearby Enemy
20% increased Movement Speed if you've Killed Recently 
Opportunistic is a notable Ascendancy passive skill for the Assassin. It grants bonus movement speed if you've killed recently and causes your critical strikes to be unable to get reflected. It also grants increased damage and causes critical strikes taken to not deal extra damage while there is only one enemy nearby.