Assassinate

A ninja with this master trick can kill foes that are unable to defend themselves. To attempt to assassinate a target, the ninja must first study her target for 1 round as a standard action. On the following round, if the ninja makes a sneak attack against the target and the target is denied its Dexterity bonus to AC, the sneak attack has the additional effect of possibly killing the target. This attempt automatically fails if the target recognizes the ninja as an enemy. If the sneak attack is successful and the target of this attack fails a Fortitude save, it dies. The DC of this save is equal to 10 + 1/2 the ninja's level + the ninja's Charisma modifier. If the save is successful, the target still takes the sneak attack damage as normal, but it is immune to that ninja's assassinate ability for 1 day.