You can equip the assassin with poison, which increases its CR by +1. On the assassin's first successful attack, the target must succeed on a Constitution check, DC [10 + CR], or take [CR x 1d6] damage and become Weakened for the rest of the combat. On a success, it takes only half damage and is not Weakened.

An attack similar to the Rogue's Sneak Attack that must be made from behind or by surprise. The creature gains a +5 bonus to its attack roll and adds [2d6 per rank] to its damage. The creature also gains a +5 bonus to Stealth checks.