Damage from your Critical Strikes cannot be Reflected 25% more Damage while there is at most one Rare or Unique Enemy nearby 20% reduced Damage taken while there are at least two Rare or Unique Enemies nearby 
Opportunistic is a notable Ascendancy passive skill for the Assassin. It causes your critical strikes to be unable to get reflected. It also grants more damage if there is one or no rare or unique enemies nearby or damage reduction if there are at least two rare or unique enemies nearby.
No longer grants 100% increased damage while there is only one enemy nearby, nor causes you to take no extra damage from critical strikes while there is only one enemy nearby. Now grants 20% more damage (Multiplicative! Again!) while there is at most one Rare or Unique enemy nearby. Also reduces damage taken by 10% while there are at least two Rare or Unique enemies nearby.